Material for denture base, denture base, method of manufacturing the denture base, plate denture, and method of manufacturing the plate denture

ABSTRACT

Disclosed is a material for a denture base containing a polymer component and containing an acrylic resin.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.15/116,124, which is the National Stage of International Application No.PCT/JP2015/053129, filed Feb. 4, 2015, the disclosures of which areincorporated herein by reference in its entirety. Further, thisapplication claims priority from Japanese Patent Application No.2014-020634 filed Feb. 5, 2014, and No. 2014-265370 filed on Dec. 26,2014, the disclosures of which are incorporated herein by reference inits entirety.

TECHNICAL FIELD

The present invention relates to a material for a denture base, adenture base, method of manufacturing the denture base, a plate denture,and a method of manufacturing the plate denture.

BACKGROUND ART

There has been a widespread use of a plate denture provided withartificial teeth and a denture base for fixing the artificial teeththereto. As the denture base, a polymer-containing denture base has beenwidely used.

Conventionally, the polymer-containing denture base has beenmanufactured by a method of pouring a curable resin into a gypsum moldconstituted of an upper mold and a lower mold and then curing thecurable resin (by photopolymerization or thermal polymerization, forexample).

There has been recently known a method of cutting a cured polymer(resin) with the use of a CAD (Computer Aided Design)/CAM (ComputerAided Manufacturing) system, for example, and thereby manufacturing theabove-described denture base (see, for example, WO 2010-058822 andJapanese National-Phase Publication (JP-A) No. 2006-521136).

SUMMARY OF INVENTION Technical Problem

When a plate denture provided with a polymer-containing denture base isused for a long period of time, the denture base may likely be broken.

According to the consideration made by the inventors of this invention,it was found that an ease of occurrence of the breakage of a denturebase is correlated with the durability (yield point strength in acompression test) of the denture base, and as the durability (yieldpoint strength in a compression test) of the denture base becomeshigher, the denture base tends to be less likely to be broken.

As a result of further consideration made by the inventors of thisinvention, it is found out that even when that a hard material (amaterial having a high elastic modulus) is used as a material for adenture base in order to enhance the durability of a denture base formedof the material, the denture base formed of the material may likely lackdurability (yield point strength in a compression test).

It is preferable to use a hard material as a material for a denturebase, in view of practical utility of a plate denture with a denturebase, and workability when a denture base is manufactured.

In view of the above, an object of the present invention is to achievethe following purposes.

Namely, an object of this invention is to provide a material for adenture base excellent in durability (yield point strength in acompression test) when a denture base is formed of the material.

A further object of this invention is to provide a denture baseexcellent in durability (yield point strength in a compression test) anda method of manufacturing the denture base.

A furthermore object of this invention is to provide a plate denture,which is provided with a denture base excellent in durability (yieldpoint strength in a compression test) and can prevent the denture basefrom being broken by use for a long period of tune.

Solution to Problem

In addition, an object of this invention is to provide a material for adenture base excellent in hardness (flexural modulus) and durability(yield point strength in a compression test) when a denture base isformed of the material.

A further object of this invention is to provide a denture baseexcellent in durability (yield point strength in a compression test)that can be produced using a material for a denture base excellent inhardness (flexural modulus), and a method of manufacturing the denturebase.

Furthermore, an object of this invention is to provide a plate denture,which has a denture base excellent in durability (yield point strengthin a compression test) that can be produced using a material for adenture base excellent in hardness (flexural modulus), and can preventthe denture base from being broken by use for a long period of time.

Solution to Problem

Specific means for achieving the above objects are as follows.

<1> A material for a denture base containing a polymer component, thepolymer component having a weight average molecular weight of 1,200,000or more and containing an acrylic resin.

<2> The material for a denture base according to <1>, wherein the weightaverage molecular weight of the polymer component is 1,500,000 or more.

<3> The material for a denture base according to <1> or <2>, wherein theweight average molecular weight of the polymer component is 2,500,000 ormore.

<4> The material for a denture base according to any one of <1> to <3>,wherein when the material for a denture base is formed into a test piecehaving a length of 80 mm, a width of 10 mm, and a thickness of 4 mm, thetest piece exhibits 110 MPa or more of flexural strength measured by athree-point flexural test in accordance with JIS K7171 (2008) underconditions of a testing speed of 2 mm/min and a length of a support spanof 64 mm.

<5> The material for a denture base according to <4>, wherein theflexural strength is 200 MPa or less.

<6> The material for a denture base according to any one of <1> to <5>,wherein when the material for a denture base is formed into asingle-notched test piece which is provided with a notch having theshape A prescribed by JIS K7111-1 (2012) and has a length of 80 mm, awidth of 10 mm, a remaining, width of 8 mm, and a thickness of 4 mm, thetest piece exhibits 1.41 kJ/m² or more of impact strength measured byCharpy impact test under the condition of edgewise impact in accordancewith MS K7111-1 (2012).

<7> The material for a denture base according to any one of <1> to <3>,wherein when the material for a denture base is formed into asingle-notched test piece which is provided with a notch having theshape A prescribed by JIS K7111-1 (2012) and has a length of 80 mm, awidth of 10 mm, a remaining width of 8 mm, and a thickness of 4 mm, thetest piece exhibits 2.0 kJ/m² or more of impact strength measured byCharpy impact test under the condition of edgewise impact in accordancewith JIS K7111-1 (2012), and when the material for a denture base isformed into a test piece having a length of 80 mm, a width of 10 mm, anda thickness of 4 mm, the test piece exhibits 100 MPa or more of flexuralstrength measured by a three-point flexural test in accordance with JISK7171 (2008) under conditions of a testing speed of 2 mm/min and alength of a support span of 64 mm.

<8> The material for a denture base according to <8>, wherein thepolymer component further contains a rubber.

<9> The material for a denture base according to <8>, wherein the rubbercontains a polymer obtained by graft polymerization of a rubbery polymerhaving a cross-linked structure with a thermoplastic resin component.

<10> The material for a denture base according to <8> or <9>, whereinthe rubber contains a polymer obtained by graft polymerization of abutadiene (co)polymer with a thermoplastic resin component.

<11> The material for a denture base according to any one of <8> to<10>, wherein a content of the rubber is from 1% by mass to 10% by massbased on a total amount of the material for a denture base.

<12> The material for a denture base according to any one of <8> to<11>, wherein a content of the rubber is from 1% by mass to 7% by massbased on a total amount of the material for a denture base.

<13> The material for a denture base according to any one of <1> to<12>, wherein a content of the acrylic resin is 90% by mass or morebased on a total amount of the material for a denture base.

<14> The material for a denture base according to any one of <1> to<13>, wherein the acrylic resin is a polymer obtained by polymerizing amonomer component containing a monofunctional acrylic monomer in anamount of 95% by mass or more.

<15> The material for a denture base according to <14>, wherein themonofunctional acrylic monomer is at least one selected from the groupconsisting of methacrylic acid and methacrylic acid alkyl ester.

<16> The material for a denture base according to <14>, wherein themonofunctional acrylic monomer consists of methacrylic acid andmethacrylic acid alkyl ester, and an amount of the methacrylic acidbased on a total amount of the methacrylic acid and the methacrylic acidalkyl ester is from 0.1% by mass to 15% by mass.

<17> The material for a denture base according to any one of <1> to<15>, wherein the acrylic resin is polymethyl methacrylate.

<18> A material for a denture base, wherein when the material for adenture base is formed into a test piece having a length of 80 mm, awidth of 10 mm, and a thickness of 4 mm, the test piece exhibits 110 MPaor more of flexural strength measured by a three-point flexural test inaccordance with JIS K7171 (2008) under conditions of a testing speed of2 mm/min and a length of a support span of 64 mm, and the material for adenture base contains a polymer component that is at least one selectedfrom the group consisting of a sulfone-based resin and an ether ketoneresin.

<19> The material for a denture base according to <18>, wherein theflexural strength is 200 MPa or less.

<20> The material for a denture base according to <18> or <19>, whereinwhen the material for a denture base is formed into a single-notchedtest piece which is provided with a notch having the shape A prescribedby JIS K7111-1 (2012) and has a length of 80 mm, a width of 10 mm, aremaining width of 8 mm, and a thickness of 4 mm, the test pieceexhibits 1.41 kJ/m² or more of impact strength measured by Charpy impacttest under the condition of edgewise impact in accordance with JISK7111-1 (2012).

<21> The material for a denture base according to any one of <18> to<20>, wherein the polymer component is at least one selected from thegroup consisting of polyphenyl sulfone and polyether ether ketone.

<22> The material for a denture base according to any one of <1> to<21>, wherein a content of inorganic fibers and inorganic whiskers is0.5% by mass or less, based on the total amount of the material for adenture base.

<23> The material for a denture base according to any one of <1> to<22>, wherein the material for a denture base is a block body having athickness of from 10 mm to 40 mm.

<24> The material for a denture base according to <23>, wherein thematerial for a denture base is used in manufacturing a denture base bycuffing.

<25> A denture base containing the material for a denture base accordingto any one of <1> to <22>.

<26> A denture base obtained by cutting the material for a denture baseaccording to <23>.

<27> A plate denture comprising the denture base according to <25> or<26> and an artificial tooth fixed to the denture base.

<28> A method of manufacturing a denture base comprising a step ofcutting the material for a denture base according to <23> to obtain adenture base.

<29> The denture base manufacturing method according to <28>, whereinthe cutting step is a step of cutting the material for a denture basewith the use of a CAD/CAM system to obtain a denture base.

<30> A method of manufacturing a plate denture including:

a step of cutting the material for a denture base according to <23> toobtain a denture base; and

a step of fixing an artificial tooth to the denture base.

Advantageous Effects of Invention

<31> A material for a denture base containing a polymer componentcontaining an acrylic resin,

wherein, when the material for a denture base is formed into a testpiece having a length of 80 mm, a width of 10 mm, and a thickness of 4mm, the test piece exhibits 110 MPa. or more of flexural strengthmeasured by a three-point flexural test in accordance with JIS K7171(2008) under conditions of a testing speed of 2 mm/min and a length of asupport span of 64 mm, and

wherein, when the material for a denture base is formed into a notchedtest piece having a length of 39 mm, a height of 8 mm, and a width of 4mm, the test piece exhibits 1.9 MPa·m^(1/2) or more of maximum stressintensity factor measured by a fracture toughness test in accordancewith a flexural test in accordance with JIS 16501 (2012) under acondition of a testing speed of 1 mm/min, and exhibits 900 J/m² or moreof total work of fracture.

<32> The material for a denture base according to <31>, wherein theflexural strength is 200 MPa or less.

<33> The material for a denture base according to <31> or <32>, whereinthe maximum stress intensity factor is 3.5 MPa·m^(1/2) or less, and thetotal work of fracture is 2500 J/m² or less.

<34> The material for a denture base according to any one of <31> to<33>, wherein, when the material for a denture base is formed into asingle-notched test piece which is provided with a notch having a shapeA prescribed by JIS K7111-1 (2012) and has a length of 80 mm, a width of10 mm, a remaining width of 8 mm, and a thickness of 4 mm, the testpiece exhibits 1.6 kJ/m² or more of impact strength measured by a Charpyimpact test under a condition of edgewise impact in accordance with JISK7111-1 (2012).

<35> The material for a denture base according to any one of <31> to<34>, wherein a weight average molecular weight of the polymer componentis 1,200,000 or more.

<36> The material for a denture base according to any one of <31> to<35>, wherein the polymer component further contains a rubber.

<37> The material for a denture base according to <36>, wherein therubber contains a graft polymer obtained by graft polymerization of arubbery polymer having a cross-linked structure with a thermoplasticresin component.

<38> The material for a denture base according to <36> or <37>, whereinthe rubber contains a graft polymer obtained by graft polymerization ofa butadiene (co)polymer with a thermoplastic resin component.

<39> The material for a denture base according to any one of <36> to<38>, wherein a content of the rubber is from 1% by mass to 10% by massbased on a total amount of the material for a denture base.

<40> The material for a denture base according to any one of <31> to<39>, wherein a content of the acrylic resin is 90% by mass or morebased on a total amount of the material for a denture base.

<41> The material for a denture base according to any one of <31> to<40>, Wherein the acrylic resin is a polymer comprising a structuralunit derived from a monofunctional acrylic monomer in an amount of 95%by mass or more.

<42> The material for a denture base according to <41>, wherein themonofunctional acrylic monomer is at least one selected from the groupconsisting of methacrylic acid and methacrylic acid alkyl ester.

<43> The material for a denture base according to <41>, wherein themonofunctional acrylic monomer consists of methacrylic acid andmethacrylic acid alkyl ester, and an amount of the methacrylic acidbased on a total amount of the methacrylic acid and the methacrylic acidalkyl ester is from 0.1% by mass to 15% by mass.

<44> The material for a denture base according to any one of <31> to<43>, wherein the acrylic resin is a co-polymer of methacrylic acid andmethyl methacrylate.

<45> A denture base containing the material for a denture base accordingto any one of <31> to <44>.

<46> A plate denture comprising the denture base according to <45> andan artificial tooth fixed to the denture base.

<47> A method of manufacturing a denture base comprising a step ofcutting the material for a denture base according to any one of <31> to<44> to obtain a denture base.

<48> A method of manufacturing a plate denture comprising:

a step of cutting the material for a denture base according to any oneof <31> to <44> to obtain a denture base; and

a step of fixing an artificial tooth to the denture base.

The present invention provides a material for a denture base excellentin durability (yield point strength in a compression test) when adenture base is formed of the material.

The invention further provides a denture base excellent in durability(yield point strength in a compression test) and a method ofmanufacturing the denture base.

The invention furthermore provides a plate denture, which is providedwith a denture base excellent in durability (yield point strength in acompression test) and can prevent the denture base from being broken byuse for a long period of time.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view conceptually showing an example of a platedenture of the present invention.

FIG. 2 is a graph showing an example of a relationship between minuteflexural strength of a denture base and flexural strength of a materialfor a denture base in this invention.

FIG. 3 is a graph showing an example of a relationship between minuteimpact strength of a plate denture and impact strength of a material fora denture base in this invention.

FIG. 4 is a graph showing an example of a relationship between a minutemaximum stress intensity factor of a denture base and a maximum stressintensity factor of a material for a denture base.

FIG. 5 is a graph showing an example of a relationship between a minutetotal work of fracture of a denture base and a total work of fracture ofa material for a denture base.

DESCRIPTION OF EMBODIMENTS

In this specification, numerical ranges depicted with “from” and “to”represent ranges inclusive of the numbers that respectively appear atthe left and right of “to” as the minimum value and the maximum value,respectively. For example, “from a numerical value A to a numericalvalue B” is synonymous with “a numerical value A or more and a numericalvalue B or less”.

Further, in this specification, yield point strength in a compressiontest is also merely referred to as “yield point strength”. Namely, inthe specification, the mere term “yield point strength” means the yieldpoint strength in a compression test.

[Material for Denture Base]

Hereinafter, first and second embodiments of a material for a denturebase of the present invention will be described.

First Embodiment

A material for a denture base of the first embodiment contains a polymercomponent having a weight average molecular weight of 1,200,000 or moreand containing an acrylic resin.

According to the material for a denture base of the first embodiment,the durability (indicates yield point strength in a compression test andis hereinafter sometimes referred to as “yield point strength”) of adenture base formed of this material is enhanced. Consequently, breakageof the denture base due to use for a long period of time is reduced.Although this reason is not clear, the reason is assumed as follows.

Namely, the denture base has a complex shape corresponding to an oralcavity of a denture user. Thus, according to an occlusal state of thedenture user, a force applied to a plate denture is locally concentratedat a portion of the denture base. Therefore, it is considered that evenwhen a hard material (a material having a high elastic modulus) is usedas a material for a denture base, the denture base may be broken.Further, it is also considered that a minute clack occurs in the denturebase due to some cause during use, the denture base is likely to bebroken from the crack as a starting point.

Regarding those points, when as a material for a denture base, it isconsidered that when there are used not merely a “hard material” (amaterial having a high elastic modulus) but also a material having highdurability against multidirectional forces or a material in which crackhardly occurs even when multidirectional forces are applied thereto,that is, a material in which the flexural strength in a three-pointflexural test (hereinafter also referred to as the “flexural strength”)is high, the durability (yield point strength) of a denture base formedof this material can be enhanced, and furthermore, when a plate dentureis used for a long period of time, a denture base of the plate denturecan be prevented from being broken.

Regarding the flexural strength, the present inventors found that amaterial for a denture base containing a polymer component having aweight average molecular weight of 1,200,000 or more and containing anacrylic resin exhibits high flexural strength.

Thus, according to the material for a denture base of the firstembodiment, it is considered that the durability (yield point strength)of a denture base formed of this material can be enhanced, andfurthermore, when a plate denture is used for a long period of time, adenture base of the plate denture can be prevented from being broken.

Further, according to the material for a denture base of the firstembodiment, since the durability (yield point strength) of a denturebase formed of this material can be enhanced, it is possible tomanufacture a thin denture base (that is, a lightweight denture baseexcellent in wearing feeling) as compared to denture bases manufacturedby a conventional method using a gypsum mold.

Here, the “flexural strength in a three-point flexural test” of amaterial for a denture base indicates flexural strength measured by athree-point flexural test in accordance with JIS K7171 (2008) under theconditions of a testing speed of 2 mm/min and a length of the supportspan of 64 mm when the material for a denture base is formed into a testpiece having a length of 80 mm, a width of 10 m, and a thickness of 4 mm(the same is applied to the following description).

The flexural strength in the three-point flexural test can be measuredusing a 5-hook flexural test machine model 2001-5 manufactured byIntesco Co., Ltd., for example.

The test piece can be taken from the material for a denture base of thefirst embodiment by cutting or the like.

Hereinafter, the “flexural strength in a three-point flexural test” isalso merely referred to as “flexural strength”.

Further, hereinafter, “a length of 80 mm, a width of 10 mm, and athickness of 4 mm” is also referred to as “80 mm×10 mm×4 mm size”.

The weight average molecular weight (Mw) of the polymer component in thefirst embodiment is 1,200,000 or more.

When Mw of the polymer component is 1,200,000 or more, the flexuralstrength of a material for a denture base is enhanced, and furthermore,the durability (yield point strength) of a denture base formed of thismaterial is enhanced.

Further, when Mw of the polymer component in the first embodiment is1,200,000 or more, it is advantageous in cutting workability when adenture base is manufactured by cutting (for example, it is advantageousin that at least one of cracking and chipping is reduced duringcutting).

In view of further enhancement of the flexural strength, the Mw of apolymer component is preferably 1,500,000 or more, more preferably2,000,000 or more, still more preferably 2,500,000 or more, even morepreferably 3,000,000 or more, further more preferably 3,500,000 or more,still further more preferably 4,000,000 or more.

Further, in view of productivity, it is preferable that the Mw of apolymer component is adjusted to 8,000,000 or less.

In the flexural strength of the material for a denture base of the firstembodiment, in view of further enhancement of the durability (yieldpoint strength) of a denture base formed of this material, the flexuralstrength of the material for a denture base is preferably 100 MPa ormore, more preferably 110 MPa or more, still more preferably 120 MPa ormore, even more preferably more than 120 MPa, further more preferably121 MPa or more.

Meanwhile, although the upper limit of the flexural strength is notparticularly limited, in view of cutting workability, the flexuralstrength is preferably 200 MPa or less.

In the material for a denture base of the first embodiment, in view ofimpact resistance of a denture base formed of this material, the impactstrength is preferably 1.41 kJ/m² or more.

Here, the “impact strength” of a material for a denture base indicatesCharpy impact strength measured by Charpy impact test under thecondition of edgewise impact in accordance with JIS K7111-1 (2012) whena material for a denture base is formed into a single-notched test piecewhich is provided with a notch having the shape A prescribed by JISK7111-1 (2012) and has a length of 80 mm, a width of 10 mm, a remainingwidth of 8 mm, and a thickness of 4 mm (the same is applied to thefollowing description).

The impact strength (Charpy impact strength) can be measured using, forexample, an impact tester DG-UB equipped with a constant temperaturebath manufactured by Toyo Seiki Seisaku-Sho Ltd.

The single-notched test piece can be taken from the material for adenture base of the first embodiment by cutting or the like.

When the impact strength is 1.41 kJ/m² or more, the impact resistance ofa denture base formed of the material for a denture base of the firstembodiment is further enhanced.

The impact strength is more preferably 2.0 kJ/m² or more.

Although the upper limit of the impact strength is not particularlylimited, the upper limit may be 11.0 kJ/m², for example. The upper limitof the impact strength may be 6.0 kJ/m² or 4.0 kJ/m².

In the material for a denture base of the first embodiment, the flexuralmodulus is preferably from 2500 MPa to 3700 MPa, more preferably from2650 MPa to 3700 MPa, still more preferably from 2700 MPa to 3700 MPa.

Further, the upper limit of the flexural modulus may be 3200 MPa.

Here, the “Textual modulus” indicates a flexural modulus measured by athree-point flexural test under the same conditions as theabove-described “flexural strength”. The flexural modulus is calculatedby a “secant method”.

<Polymer Component>

The polymer component in the first embodiment contains an acrylic resinand has a weight average molecular weight (Mw) of 1,200,000 or more.

The Mw referred to herein means the Mw of the (entire) polymercomponent.

Needless to say, when the polymer component is formed only of theacrylic resin, the Mw of the polymer component matches the Mw of theacrylic resin.

The preferable ranges of the Mw of the polymer component are asdescribed above.

In the polymer in the first embodiment, the molecular weightdistribution (Mw/Mn) is preferably from 1.1 to 20, more preferably from1.1 to 15, still more preferably from 1.1 to 10, even more preferablyfrom 1.1 to 7.0, further more preferably from 1.5 to 60, particularlypreferably from 2.0 to 5.5.

In this specification, the weight average molecular weight (Mw) and themolecular weight distribution (Mw/Mn) indicate respective Valuesmeasured using a gel permeation chromatograph (GPC) by the following GPCmeasuring method.

—GPC Measuring Apparatus—

LC-10AD manufactured by Shimadzu Corporation

—Column—

Shodex K-806L 30 cm×2

—Preparation of Sample—

A polymer component to be measured is dissolved in a solvent(tetrahydrofuran) at room temperature (20° C. to 30° C.) to prepare asample solution having a concentration of 0.1% (w/v).

—Measurement Conditions—

100 μL of the sample solution is introduced into the column at a columntemperature of 40° C. and a flow rate of 1.0 mL/min. with a mobile phase(for example, tetrahydrofuran).

The sample concentration in the sample solution separated in the columnis measured with a differential refractometer (RI-101). A universalcalibration curve is created with a polymethylmethacrylate standardsample, and the weight average molecular weight (Mw), a number averagemolecular weight (Mn), and the molecular weight distribution (Mw/Mn) ofthe polymer component are calculated.

Analysis can be performed using data processing software Empower 2(manufactured by Waters Corporation), for example.

From the standpoint of ease of realization of the fact that the weightaverage molecular weight (Mw) of the polymer component is 1,200,000 ormore, as the acrylic resin contained in the polymer component, anacrylic resin obtained by polymerizing a monomer, an acrylic resinobtained by polymerizing an oligomer or a prepolymer, or an acrylicresin obtained by polymerizing a mixture of an oligomer or a prepolymerand a monomer is preferably used. As the oligomer or the prepolymer, anoligomer or a prepolymer having fluidity at room temperature isparticularly preferably used.

A usual acrylic resin for dentures is an acrylic resin obtained bypolymerizing a mixture of a polymer in a solid state at room temperatureand a monomer.

However, when as the acrylic resin in the first embodiment, the acrylicresin obtained by polymerizing the mixture of a polymer in a solid stateat room temperature and a monomer is used, there is a tendency that itis difficult that the Mw of the polymer component containing the acrylicresin is 1,200,000 or more (preferably 1,500,000 or more).

For example, a denture base formed of the usual acrylic resin fordentures is manufactured by mixing an acrylic polymer, which is a powderin a solid state at room temperature and has a relatively high molecularweight, a monomer for an acrylic compound, and a polymerizationinitiator, polymerizing the mixture to a state with fluidity, thenpouring the polymerized mixture into a gypsum mold or the like, andcuring the mixture by heating or the like. This method of manufacturinga denture base is usually performed by a dental technician, and sincethe polymerization rate is high, the method has an advantage that it isconvenient for the dental technician. However, in this method, since adifference in molecular weight between a powder as a starting rawmaterial and a monomer is large, it is assumed that the Mw of theacrylic resin is hardly increased.

With respect to the above usual method, for example, only an oligomer ora prepolymer having fluidity at room temperature, or a mixture obtainedby adding a monomer to an oligomer or a prepolymer is polymerized overseveral days to several weeks near the polymerization temperature of theoligomer or the prepolymer, such that a degree of polymerization anduniformity of polymerization can be enhanced. Consequently, it isconsidered that the Mw of the acrylic resin can be set to 1,200,000 ormore, and furthermore, the Mw of the polymer component can be set to1,200,000 or more.

When the polymer component in the first embodiment contains a rubber, anoligomer or a prepolymer, or a mixture obtained by adding a monomer toan oligomer or a prepolymer is mixed with a rubber, and then theresultant mixture may be polymerized.

(Acrylic Resin)

A polymer component contains an acrylic resin.

Since the material for a denture base in the first embodiment contains ahighly transparent acrylic resin, the material has an advantage that thedegree of freedom of coloring is high. Further, since the material for adenture base in the first embodiment contains an acrylic resin, thematerial has an advantage that the adhesiveness to a commerciallyavailable acrylic artificial tooth is excellent.

The polymer component in the first embodiment may contain only one kindor two or more kinds of acrylic resin.

In this specification, an acrylic resin indicates a polymer containingat least one structural unit selected from the group consisting of astructural unit derived from acrylic acid, a structural unit derivedfrom methacrylic acid, a structural unit derived from acrylic acidester, and a structural unit derived from methacrylic acid ester.

Namely, the acrylic resin in this specification is a polymer obtained bypolymerizing a monomer component containing at least one kind(hereinafter also referred to as an “acrylic monomer”) selected from thegroup consisting of acrylic acid, methacrylic acid, acrylic acid ester,and methacrylic acid ester.

An acrylic monomer as at least a portion of a raw material of an acrylicresin may be a monofunctional acrylic monomer or a polyfunctionalacrylic monomer.

Examples of the monofunctional acrylic monomer include acrylic acid,methacrylic acid, acrylic acid ester containing one acryloyl group in amolecule, and methacrylic acid ester containing one methacryloyl groupin a molecule.

Examples of the polyfunctional acrylic monomer include acrylic acidester containing two or more acryloyl groups in a molecule andmethacrylic acid ester containing two or more methacryloyl groups in amolecule.

More specific examples of the acrylic resin include a homopolymer ofacrylic acid, a homopolymer of methacrylic acid, a homopolymer ofacrylic acid ester, a homopolymer of methacrylic acid ester, a copolymerof acrylic acid and another monomer (for example, acrylic acid ester,methacrylic acid, methacrylic acid ester, or α-olefin (for example,ethylene)), a copolymer of methacrylic acid and another monomer (forexample, acrylic acid, acrylic acid ester, methacrylic acid ester, orα-olefin (for example, ethylene)), a copolymer of acrylic acid ester andanother monomer (for example, acrylic acid, methacrylic acid,methacrylic acid ester, or α-olefin (for example, ethylene)), and acopolymer of methacrylic acid ester and another monomer (for example,acrylic acid, acrylic acid ester, methacrylic acid, or α-olefin (forexample, ethylene)).

The acrylic acid ester is preferably an acrylic acid alkyl ester, morepreferably a linear alkyl ester or branched-chain alkyl ester of acrylicacid, and still more preferably the linear alkyl ester of acrylic acid.

Further, it is preferable that the acrylic acid ester contains nohalogen atom such as fluorine atoms and chlorine atoms.

The acrylic acid ester is more preferably an acrylic acid alkyl ester inwhich the number of carbons of an alkyl group contained at an alkylester is 1 to 4, still more preferably methyl acrylate or ethylacrylate, and particularly preferably methyl acrylate.

The methacrylic acid ester is preferably a methacrylic acid alkyl ester,more preferably a linear alkyl ester or branched-chain alkyl ester ofmethacrylic acid, and still more preferably the linear alkyl ester ofmethacrylic acid.

Further, it is preferable that the methacrylic acid ester contains nohalogen atom such as fluorine atoms and chlorine atoms.

The methacrylic acid ester is more preferably a methacrylic acid alkylester in which the number of carbons of an alkyl group contained at analkyl ester is 1 to 4, still more preferably methyl methacrylate orethyl methacrylate, and particularly preferably methyl methacrylate.

In view of reactivity and productivity, the acrylic resin is preferablya polymer obtained by polymerizing a monomer component containing amonofunctional acrylic monomer.

The acrylic resin is more preferably a polymer obtained by polymerizinga monomer component containing 50% by mass or more (preferably 80% bymass or more, still more preferably 90% by mass or more, even morepreferably 95% by mass or more) of a monofunctional acrylic monomer.

The monofunctional acrylic monomer is preferably at least one kindselected from the group consisting of acrylic acid, methacrylic acid,acrylic acid alkyl ester, and methacrylic acid alkyl ester.

In view of physical properties (heat resistance) of a material for adenture base and a denture base, the monofunctional acrylic monomer ismore preferably at least one kind selected from the group consisting ofa methacrylic acid and a methacrylic acid alkyl ester.

The respective preferable ranges of the acrylic acid alkyl ester and themethacrylic acid alkyl ester are the same as described above.

As preferred embodiments of the acrylic resin, an embodiment in whichthe monofunctional acrylic monomer is a methacrylic acid alkyl ester isexemplified. Hereinafter, the acrylic resin according to this embodimentis also referred to as an “acrylic resin X”.

The acrylic resin X is preferably a polymer obtained by polymerizing amonomer component containing methyl methacrylate (namely, this polymeris a polymer containing a structural unit derived from methylmethacrylate) and particularly preferably a homopolymer of methylmethacrylate (polymethyl methacrylate, that is, polymethylmethacrylate(PMMA)).

As another preferred embodiment of the acrylic resin, there isexemplified an embodiment in which the monofunctional acrylic monomerconsists of methacrylic acid and methacrylic acid alkyl ester, and anamount of methacrylic acid based on the total amount of methacrylic acidmethacrylic acid alkyl ester is more than 0% by mass and 15% by mass orless (more preferably from 0.1% by mass to 15% by mass, still morepreferably from 1% by mass to 15% by mass, even more preferably from 5%by mass to 15% by mass). Hereinafter, the acrylic resin according tothis embodiment is also referred to as an “acrylic resin Y”.

As compared to the acrylic resin X (for example, PMMA), the acrylicresin Y is advantageous in terms of the flexural strength of a materialfor a denture base and durability (yield point strength in a compressiontest) of a denture base.

As the acrylic resin Y, a methacrylic acid alkyl ester-methacrylic acidcopolymer in which the content of the structural unit derived frommethacrylic acid is 15% by mass or less is particularly preferably used.

The polymer component in the first embodiment may contain only one kindof acrylic resin or may contain two or more kinds of acrylic resin.

Further, the polymer component in the first embodiment may contain aresin other than the acrylic resin.

Incidentally, the content of the acrylic resin in the material for adenture base in the first embodiment (when two or more kinds of acrylicresin are used, the content is a total content) based on the totalamount of the material for a denture base is preferably 60% by mass ormore, more preferably 80% by mass or more, still more preferably 90% bymass or more, even more preferably 95% by mass or more, particularlypreferably 99% by mass or more.

(Rubber)

The polymer component in the first embodiment may contain a rubber.

When the polymer component in the first embodiment contains a rubber,the impact strength of the material for a denture base is furtherenhanced, and the impact resistance of a denture base formed of thismaterial is further enhanced.

Examples of the kind of rubber include acrylic rubber, butadiene rubber,butadiene-acrylic rubber, butadiene-styrene rubber, and silicone rubber.

When the polymer component in the first embodiment contains a rubber,the kind of rubber may be suitably selected in consideration of physicalproperties. Considering a balance among various properties such ashardness and impact resistance, butadiene rubber or butadiene-acrylicrubber is preferably used.

When the polymer component in the first embodiment contains a rubber,only one kind of rubber or two or more kinds of rubbers may be containedin the polymer component.

It is preferable that the rubber contains a polymer obtained by graftpolymerization of a rubbery polymer (preferably a rubbery polymer havinga cross-linked structure) with a thermoplastic resin component.

The thermoplastic resin component is not particularly limited as long asit is a monomer component capable of graft polymerizing with a rubberypolymer. Examples of the thermoplastic resin component include anaromatic vinyl compound, a vinyl cyanide compound, a (meth)acrylic acidester compound, a (meth)acrylic acid compound, an N-substitutedmaleimide compound, an α,β-unsaturated carboxylic acid compound, andanhydrides thereof (for example, maleic anhydride, etc.). These monomercomponents may be used in one kind alone, or in two or more kinds incombination.

Here, “(meth)acrylic acid” is a concept including both acrylic acid andmethacrylic acid (the same is applied to the following description).

Examples of the rubbery polymer include an acrylic (co)polymer, abutadiene (co)polymer, and a silicone-based polymer. Among them, abutadiene (co)polymer is preferably used. When the rubbery component isa butadiene (co)polymer, the impact strength of the material for adenture base is further enhanced, and the impact resistance of thedenture base formed of this material is further enhanced.

Here, “(co)polymer” is a concept including both a homopolymer and acopolymer (the same is applied to the following description).

As the acrylic (co)polymer, a copolymer obtained by polymerizing amixture of one or more kinds of acrylic acid alkyl esters in which thenumber of carbons of the alkyl group is from 2 to 8 and one or morekinds of polyfunctional monomers is preferably used.

The mixture may contain, if necessary, a copolymerizable monomer such asstyrene; a styrene derivative such as α-methyl styrene and vinyltoluene; acrylonitrile; and methyl methacrylate (styrene or a mixture ofstyrene and a styrene derivative is preferably contained).

Examples of the acrylic acid alkyl ester in which the number of carbonsof the alkyl group is from 2 to 8 include ethyl acrylate, n-butylacrylate, and 2-ethylhexyl acrylate. Among them, n-butyl acrylate ismore preferably used.

Examples of a polyfunctional monomer include a well-known acrylicpolyfunctional monomer and a well-known polyvalent aromatic vinylmonomer (for example, divinylbenzene).

The amount of a component constituting the acrylic (co)polymer is notparticularly limited. The acrylic (co)polymer is preferably a copolymerobtained by copolymerizing 50.0% by mass to 99.9% by mass of an acrylicacid alkyl ester, 0.1% by mass to 10% by mass of a polyfunctionalmonomer; and 0% by mass to 49.9% by mass of a copolymerizable monomer.

The rubber obtained by graft polymerization of an acrylic (co)polymerwith a thermoplastic resin component is commercially available, andexamples thereof include “Metablen (trademark) W-450” manufactured byMitsubishi Rayon Co., Ltd.

Examples of a butadiene (co)polymer include a butadiene-n-butyl acrylatecopolymer and a butadiene-styrene copolymer.

The butadiene (co)polymer is preferably a copolymer obtained bycopolymerizing 5% by mass or more of 1,3-butadiene and 95% by mass orless of at least one kind of monomer that is copolymerizable with1,3-butadiene.

Examples of the monomer that is copolymerizable with 1,3-butadieneinclude styrene, acrylonitrile, and the above-described acrylic acidalkyl ester in which the number of carbons of the alkyl group is from 2to 8.

In the copolymerization of the monomer that is copolymerizable with1,3-butadiene, with 1,3-butadiene, a polyfunctional monomer may be usedtogether.

Here, examples of the polyfunctional monomer include a well-knownacrylic polyfunctional monomer and a well-known polyvalent aromaticvinyl monomer (for example, divinylbenzene).

In terms of further enhancement of the impact strength of the materialfor a denture base and further enhancement of the impact resistance ofan obtained denture base, a butadiene (co)polymer is preferably abutadiene-n-butyl acrylate copolymer obtained by copolymerizingbutadiene and n-butyl acrylate.

The rubber obtained by graft polymerization of a butadiene (co)polymerwith a thermoplastic resin component is commercially available, andexamples thereof include “MUX-60” manufactured by UMG ABS, Ltd. and“KANE ACE (trademark) M-521” manufactured by Kaneka Corporation.

Examples of a silicone-based polymer include room temperature curablesilicone rubber and thermosetting silicone rubber. Specific examples ofthe silicone-based polymer include dimethyl silicone rubber, vinylmethylsilicone rubber, methylphenyl silicone rubber, and fluorosiliconerubber. As the silicone-based polymer, well-known silicone rubber may beused.

The rubber obtained by graft polymerization of a silicone-based polymerwith a thermoplastic resin component is commercially available, andexamples thereof include “Metablen (trademark) S-2001” manufactured byMitsubishi Rayon Co., Ltd.

The rubber is preferably rubber particles.

When the polymer component in the first embodiment contains rubberparticles as a rubber, the rubber particles are dispersed in an acrylicresin. Therefore, the impact strength of the material for a denture baseis further enhanced.

Examples of rubber particles include rubber particles having a monolayerstructure and rubber particles having a multilayer structure.

The rubber particles having a multilayer structure may be provided with,for example, an inner layer of a rubbery polymer, such as theabove-described acrylic (co)polymer, the above-described butadiene(co)polymer, and the above-described silicone-based polymer, and anouter layer of a resin obtained by polymerizing the above-describedthermoplastic resin component around the inner layer.

Meanwhile, a rubber in which a small amount of cross-linkablepolyfunctional monomer is copolymerized with a rubbery polymer may beused.

As the resin obtained by polymerizing a thermoplastic resin component, apolymer whose glass transition temperature is higher than roomtemperature is preferably used.

For example, acrylic rubber particles may have a monolayer structure ofa rubbery polymer mainly composed of methyl methacrylate or a multilayerstructure in which a thermoplastic resin layer mainly composed of methylmethacrylate is provided around an inner layer which is an elastic resinlayer mainly composed of acrylic acid alkyl ester such as n-butylacrylate, or well-known acrylic rubber particles may be used.

The rubber particles are more preferably rubber particles obtained bygraft polymerization of a rubbery polymer (preferably a rubbery polymerhaving a cross-linked structure) with a thermoplastic resin component.

As described above, examples of the rubbery polymer include an acrylic(co)polymer, a butadiene (co)polymer, and a silicone-based polymer.Among them, the butadiene (co)polymer is preferably used.

The average particle diameter of rubber particles is preferably in arange of from 0.03 μm to 2.0 μm. Consequently, a dispersion state of therubber particles in the material for a denture base can be suitablymaintained. The rubber particles having such a particle diameter can beproduced by an emulsion polymerization method.

When the polymer component in the first embodiment contains a rubber,the content of the rubber based on the total amount of the material fora denture base is preferably from 1% by mass to 10% by mass.

When the content of the rubber is 1% by mass or more, the impactstrength of the material for a denture base is further enhanced, and theimpact resistance of a denture base formed of this material is furtherenhanced.

When the content of the rubber is 10% by mass or less, the flexuralstrength of the material for a denture base is further enhanced, and thedurability (yield point strength in a compression test) of a denturebase formed of this material is further enhanced. Further, when thecontent of the rubber is 10% by mass or less, the flexural modulus ofthe material for a denture base is further enhanced. Therefore, thematerial for a denture base is less likely to be deformed, so thatworkability in manufacturing a denture base is further enhanced.

The upper limit of the content of the rubber is preferably 8% by mass,more preferably 7% by mass.

The lower limit of the content of the rubber is preferably 1.5% by mass,more preferably 2% by mass, particularly preferably 3% by mass.

<Other Components>

The material for a denture base in the first embodiment may containother components, if necessary.

Examples of other components include a colorant.

The colorant is not particularly limited, and pigments, dyes, coloredfibers, or the like may be used. Among them, pigments and dyes arepreferably used, and pigments are particularly preferably used.

When the material for a denture base in the first embodiment contains acolorant, the content of the colorant based on 100 parts by mass of thepolymer is preferably from 0.001 parts by mass to 0.20 parts by mass,more preferably from 0.001 parts by mass to 0.15 parts by mass, stillmore preferably from 0.001 parts by mass to 0.10 parts by mass.

When the content of the colorant is 0.20 parts by mass or less, theflexural strength of the material for a denture base of 100 MPa or moreis more easily achieved.

The material for a denture base in the first embodiment may contain amaterial simulating a blood vessel, and the content of the materialhaving a minor axis of 20 μm or more, based on 100 parts by mass of thepolymer, is preferably less than 0.001 parts by mass, more preferablyless than 0.0005 parts by mass. When the content of the material havinga minor axis of 20 μm or more is adjusted within the above range, theflexural strength is likely to be adjusted to 100 MPa or more.

When the material is fibrous, the minor axis is the average diameter offibers.

The denture base of the present invention may be obtained in thefollowing manner that an uncolored material for a denture base as thematerial for a denture base in the first embodiment is cut to obtain anuncolored denture base, and after that, the uncolored denture base iscolored with a colorant. In this case, the material for a denture basein the first embodiment does not necessarily contain a colorant.

In the material for a denture base in the first embodiment, each contentof inorganic fibers and inorganic whiskers based on the total amount ofthe material for a denture base is preferably 0.5% by mass or less, morepreferably 0.1% by mass or less, particularly preferably 0% by mass(namely, the material for a denture base in the first embodimentcontains no inorganic fiber and inorganic whisker).

Here, the fact that “each content of inorganic fibers and inorganicwhiskers based on the total amount of the material for a denture base ispreferably 0.5% by mass or less” means that the material for a denturebase in the first embodiment substantially does not contain inorganicfibers and inorganic whiskers. In this case, since a denture base to bemanufactured also contains no inorganic fiber and inorganic whisker, theeffect of obtaining extremely smooth surface of the denture base in amicroscopic view point and the effect of accordingly obtaining extremelygood wearing feeling of the denture base are expected.

In the material for a denture base in the first embodiment, the contentof the polymer component based on the total amount of the material for adenture base is preferably 90% by mass or more, more preferably 95% bymass or more, particularly preferably 99% by mass or more.

When the content of the polymer component is 90% by mass or more, theflexural strength of the material for a denture base is furtherenhanced.

The material for a denture base in the first embodiment is preferably amaterial for a denture base used in manufacturing a denture base bycutting.

In this case, the material for a denture base in the first embodiment ispreferably a block body having a thickness of from 10 mm to 40 mm inview of ease of manufacturing the material for a denture base (ease ofpolymerizing a raw material) and reducing the amount of wasted portionsin cutting out a denture base. The thickness of the block body is morepreferably from 20 mm to 40 mm.

The size of the block body is not particularly limited as long as it iscapable of obtaining a denture base by cutting.

Also, although the shape of the block body is not particularly limited,in view of ease of fixing the block body to a cutting machine, the blockbody preferably has a three-dimensional shape having an upper surfaceand a lower surface (that is, two surfaces facing each other). The blockbody more preferably has a rectangular solid shape in view of ease ofcreating a cutting program and still more preferably has a largerectangular solid shape capable of cutting a plurality of block bodiesat once.

For example, when a block body in an after-mentioned embodiment having arectangular solid shape having a size of 230 mm×190 mm×30 mm is used,four full removable denture bases can be obtained at once, and thus itis efficient.

Although a method of manufacturing the material for a denture base inthe first embodiment is not particularly limited, it is preferable touse an oligomer or to use a prepolymer or to use a mixture of anoligomer or a prepolymer and a monomer, as a raw material, and slowlypolymerize the material over about several days to one week near thepolymerization temperature. According to this manufacturing method, amaterial for a denture base containing a polymer component having a Mwof 1,200,000 or more and containing an acrylic resin is likely to bemanufactured.

When the material for a denture base in the first embodiment contains arubber, preferably, an oligomer or a prepolymer or a mixture obtained byadding a monomer to an oligomer or a prepolymer is mixed with rubber toobtain a raw material, and then the raw material is slowly polymerizedover about several days to one week near the polymerization temperatureto manufacture the material for a denture base.

The raw material may contain other components (such as a colorant and aninitiator), if necessary.

Next, a preferred embodiment of the material for a denture base in thefirst embodiment will be described.

Incidentally, the following embodiments may partially overlap with eachother.

Embodiment A

A material for a denture base in the embodiment A is a material for adenture base which contains a polymer component having a Mw of 1,500,000or more and containing an acrylic resin, and the has flexural strengthof 110 MPa or more.

The embodiment A focuses on the flexural strength of the material for adenture base, and according to the material for a denture base in theembodiment A, a denture base which is excellent particularly indurability can be manufactured.

More preferable ranges of the material for a denture base in theembodiment A are as already described as preferable ranges of thematerial for a denture base in the first embodiment, except for thecontent of a rubber (see below).

In the material for a denture base in the embodiment A, the content of arubber based on the total amount of the material for a denture base ismore preferably less than 1% by mass, particularly preferably 0% by mass(namely, the material for a denture base contains no rubber).

Embodiment B

A material for a denture base in the embodiment B is a material for adenture base which contains a polymer component having a Mw of 1,500,000or more and containing an acrylic resin, and has impact strength of 2.0kJ/m² or more and flexural strength of 100 MPa. or more.

The embodiment B focuses on the balance between the flexural strength ofthe material for a denture base and the impact strength of the materialfor a denture base, and according to the material for a denture base inthe embodiment B, a denture base which is excellent particularly in abalance between durability and impact resistance can be manufactured.

The polymer component in the embodiment B preferably contains a rubberin view of the impact strength.

The kind of a rubber and a preferable range of the content in theembodiment B are as already described as the kind of rubber and thepreferable range of the content in the first embodiment.

The flexural strength of the material for a denture base in theembodiment B is preferably 200 MPa or less in view of furtherenhancement of the impact strength. The flexural strength of thematerial for a denture base in the embodiment B is preferably 150 MPa orless, more preferably 120 MPa or less, still more preferably less than110 MPa.

Preferable ranges of the material for a denture base in the embodiment Bare as already described as preferable ranges of the material for adenture base in the first embodiment.

Embodiment C

A material for a denture base in the embodiment C contains a polymercomponent having a Mw of 1,200,000 or more and containing theabove-described acrylic resin Y, and has flexural strength of 110 MPa ormore.

The acrylic resin Y is preferably a methacrylic acid alkylester-methacrylic acid copolymer in which the content of a structuralunit derived from methacrylic acid is 15% by mass or less.

The embodiment C focuses on the flexural strength of the material for adenture base, and according to the material for a denture base in theembodiment C, a denture base which is excellent particularly indurability can be manufactured.

The polymer component in the embodiment C may contain a rubber.

When a rubber is contained in the embodiment C, the rubber and apreferable range of the content thereof are as already described as therubber and the preferable range of the content thereof in the firstembodiment.

In the material for a denture base according to the embodiment C, thecontent of the rubber based on the total amount of the material for adenture base may be less than 1% by mass or 0% by mass (namely, thematerial for a denture base may not contain a rubber).

Other preferable ranges of the material for a denture base according tothe embodiment C are as already described as the preferable ranges ofthe material for a denture base in the first embodiment.

Second Embodiment

A material for a denture base in the second embodiment has flexuralstrength of 110 MPa or more and contains a polymer component that is atleast one kind selected from the group consisting of a sulfone-basedresin and an ether ketone resin.

The “flexural strength” in the second embodiment is synonymous with the“flexural strength in a three-point flexural test” in the firstembodiment.

According to the material for a denture base in the second embodiment,there is provided an effect similar to that in the material for adenture base in the first embodiment, that is, the effect of enhancingthe durability (enhancing the yield point strength in a compressiontest) of a denture base formed of this material.

Further, according to the material for a denture base in the secondembodiment, the impact strength of the material for a denture base andthe impact resistance of a denture base formed of this material arefurther enhanced.

In the material for a denture base in the second embodiment, in view offurther enhancement of the durability (yield point strength) of adenture base formed of this material, the flexural strength ispreferably 120 MPa or more, more preferably more than 120 MPa, stillmore preferably 121 MPa or more.

Meanwhile, although the upper limit of the flexural strength is notparticularly limited, in view of cutting workability, the flexuralstrength is preferably 200 MPa or less.

In the material for a denture base in the second embodiment, the impactstrength is preferably 1.41 kJ/m² or more.

When the impact strength of the material for a denture base in thesecond embodiment is 1.41 kJ/m² or more, the impact resistance of adenture base formed of this material is further enhanced.

The “impact strength” in the second embodiment is synonymous with the“impact strength” in the first embodiment.

A preferable range of the impact strength of the material for a denturebase in the second embodiment is similar to the impact strength of thematerial for a denture base in the second embodiment.

However, the impact strength of the material for a denture base in thesecond embodiment may be 2.0 kJ/m² or more, 3.0 kJ/m² or more, or 3.5kJ/m² or more.

In the material for a denture base in the second embodiment containing asulfone-based resin, since the sulfone-based resin is highlytransparent, the material has an advantage that the degree of freedom ofcoloring is high. In this case, only one kind or two or more kinds ofsulfone-based resins may be contained in the material.

Here, the sulfone-based resin indicates a polymer containing astructural unit having a sulfonyl group (—SO₂— group) and is preferablya polymer containing a structural unit having a sulfonyl group (—SO₂—group) and a phenylene group.

More specific examples of the sulfone-based resin include polysulfone(PSU), polyether sulfone (PES), and polyphenyl sulfone (PPSU), andpolysulfone (PSU) or polyphenyl sulfone (PPSU) is preferably used.

In view of the impact strength of the material for a denture base (thatis, the impact resistance of a denture base formed of this material),polyphenyl sulfone (PPSU) is particularly preferably used.

The material for a denture base in the second embodiment containing anether ketone-based resin has an advantage that the flexural strength isparticularly high. In this case, only one kind or two or more kinds ofether ketone-based resins may be contained in the material.

Here, the ether ketone-based resin indicates a polymer containing astructural unit having an ether group (—O— group) and a ketone group(—C(═O)— group) and is preferably a polymer containing a structural unithaving an ether group (—O— group), a phenylene group, and a ketone group(—C(═O)— group).

More specific examples of the ether ketone-based resin include apolyether ether ketone (PEEK) resin, a polyether ketone (PEK) resin, apolyether ketone ketone (PEKK) resin, a polyether ether ketone ketone(PEEKK) resin, and a polyether ketone ether ketone ketone (PEKEKK)resin, and polyether ether ketone (PEEK) is particularly preferablyused.

In view of the impact strength of the material for a denture base (thatis, the impact resistance of a denture base formed of this material),the polymer component in the second embodiment is particularlypreferably at least one kind selected from the group consisting ofpolyphenyl sulfone and polyether ether ketone.

Other preferable ranges of the material for a denture base in the secondembodiment are similar to preferable ranges of the material for adenture base in the first embodiment.

Third Embodiment

The third embodiment of the invention provides a material for a denturebase excellent in hardness (flexural modulus) and durability (yieldpoint strength in a compression test) when a denture base is formed ofthe material.

Further, the third embodiment of the invention provides a denture baseexcellent in durability (yield point strength in a compression test)that can be produced using the material for denture base excellent inhardness (flexural modulus), and a method of manufacturing the denturebase.

Furthermore, the third embodiment of the invention provides a platedenture having a denture base excellent in durability (yield pointstrength in a compression test) that can be produced using the materialfor a denture base excellent in hardness (flexural modulus), and canprevent the denture base from being broken by use for a long period oftime, and a method of manufacturing the denture plate.

The material for a denture base according to the third embodimentcontains a polymer component containing an acrylic resin, wherein, Whenthe material for a denture base is formed into a test piece having alength of 80 mm, a width of 10 mm, and a thickness of 4 mm, the testpiece exhibits 110 MPa or more of flexural strength measured by athree-point flexural test in accordance with JIS K7171 (2008) underconditions of a testing speed of 2 mm/min and a length of a support spanof 64 mm, and wherein, when the material for a denture base is formedinto a notched test piece having a length of 39 mm, a height of 8 mm,and a width of 4 mm, the test piece exhibits 1.9 MPa·M^(1/2) or more ofmaximum stress intensity factor measured by a fracture toughness test inaccordance with a flexural test in accordance with JIS T6501 (2012)under the condition of a testing speed of 1 min/min, and exhibits 900J/m² or more of total work of fracture.

A material for a denture base of the third embodiment of the inventionis excellent in hardness (flexural modulus). Accordingly, a denture basehaving an excellent hardness (flexural modulus) can be produced usingthe material. Further, workability in manufacturing a denture base andutility of a denture plate with the denture base are excellent.

According to the material for a denture base of the third embodiment,the durability (yield point strength) of a denture base formed of thismaterial is enhanced. Consequently, breakage of the denture base due tolong-term use is prevented. Although this reason is not clear, thereason is assumed as similar to the reason discussed above in the firstembodiment. In addition, it is assumed that when a material in which theflexural strength in a three-point flexural test, the maximum stressintensity factor measured by a fracture toughness test, and maximumstress intensity factor measured by a fracture toughness test are highis used, the durability (yield point strength) of a denture base formedof this material can be enhanced, and furthermore, when a plate dentureis used for a long period of time, a denture base of the plate denturecan be prevented from being broken.

The material for a denture base of the third embodiment of the inventionexhibits 110 MPa or more of flexural strength measured by thethree-point flexural test as described in the first embodiment of theinvention.

When the flexural strength is 110 MPa or more, a durability (yield pointstrength in a compression test) of a denture base formed of thismaterial is significantly enhanced, and the denture base exhibitsexcellent hardness (flexural modulus).

Although the upper limit of a flexural strength is not particularlylimited, in view of cutting workability, the flexural strength ispreferably 200 MPa. or less.

The material for a denture base of the third embodiment of the inventionexhibits 1.9 MPa·m^(1/2) or more of maximum stress intensity factormeasured by a fracture toughness test in accordance with a flexural testin accordance with JIS T6501 (2012) under the condition of a testingspeed of 1 mm/min, and exhibits 900 J/m² or more of total work offracture, when the material for a denture base is formed into a notchedtest piece having a length of 39 mm, a height of 8 mm, and a width of 4min.

The test piece can be taken from the material for a denture base of thethird embodiment by a method such as cutting.

Hereinafter, the “maximum stress intensity factor measured by a fracturetoughness test” may be merely referred to as “maximum stress intensityfactor”, and “total work of fracture measured by a fracture toughnesstest” may be referred to as “total work of fracture”.

When the material for a denture base of the third embodiment of theinvention exhibits 1.9 MPa·m^(1/2) or more of maximum stress intensityfactor and 900 J/m² or more of total work of fracture, the toughness andthe durability (yield point strength) of a denture base formed from thematerial are enhanced.

Although the upper limit of the maximum stress intensity factor is notparticularly limited, in view of balancing between the maximum stressintensity factor and the hardness (flexural modulus), the upper limit ofmaximum stress intensity factor is, for example, preferably 4.0MPa·m^(1/2) or less, more preferably 3.7 MPa·m^(1/2) or less, and stillmore preferably 3.5 MPa·m^(1/2) or less.

Although the upper limit of the total work of fracture is notparticularly limited, in view of balancing between the total work offracture and the hardness (flexural modulus), the upper limit of thetotal work of fracture is, for example, preferably 3000 J/m² or less,more preferably 2500 J/m² or less, and still more preferably 2000 J/m²or less.

The maximum stress intensity factor and the total work of fracture canbe measured by, for example, UNIVERSAL TESTER 210X manufactured byINTESCO Co., Ltd.

The impact strength of the material for a denture base of the thirdembodiment can be measured by the method as described in the firstembodiment. The impact strength is preferably 1.6 kJ/m² or more. In viewof significantly enhancing the impact durability (a breaking weight in afalling ball test), the impact strength is more preferably 2.64 kJ/m² ormore, and still more preferably 2.70 kJ/m² or more.

When the impact strength is 1.6 kJ/m² or more, the impact durability (abreaking weight in a falling ball test) of a denture base formed of thematerial is enhanced.

Particularly, when the impact strength is 2.64 kJ/m² or more (preferably2.70 kJ/m² or more), the impact durability (a breaking weight in afalling ball test) of a denture base formed of the material issignificantly enhanced.

Although the upper limit of the impact strength is not particularlylimited, the upper limit may be, for example, 6.0 kJ/m² or less.

The flexural modulus of the material for a denture base of the thirdembodiment can be measured by the method as described in the firstembodiment. The flexural modulus is preferably from 2700 MPa to 4000MPa, and more preferably from 3000 μMPa to 3700 MPa.

(A Polymer Component)

The material for a denture base of the third embodiment contains apolymer component containing an acrylic resin. In the third embodiment,the weight average molecular weight (Mw) of the polymer component ispreferably 1,200,000 or more. The definition and the method formeasuring the Mw are the same as described in the first embodiment.

When the Mw of the polymer component is 1,200,000 or more, the flexuralstrength of the material for a denture base tends to be enhanced, andfurthermore, the durability (yield point strength) of a denture baseformed of this material tends to be enhanced.

Further, when the Mw of the polymer component in the third embodiment is1,200,000 or more, it is advantageous in cutting workability when adenture base is manufactured by cutting (for example, it is advantageousin that at least one of cracking and chipping is reduced duringcutting).

In view of more enhancing the flexural strength, the Mw of the polymercomponent is more preferably 1,300,000 or more, and still morepreferably 1,400,000 or more.

Further, in view of productivity, it is preferable that the Mw of thepolymer component is adjusted to 8,000,000 or less.

In the polymer component of the third embodiment, a molecular weightdistribution (Mw/Mn) is preferably from 1.1 to 7.0, more preferably from1.5 to 6.0, still more preferably from 2.0 to 5.5.

Kinds of the acrylic resin preferably used in the first embodiment canalso be preferably used in the third embodiment. An acrylic resinpreferably used in the third embodiment is a polymer obtained bypolymerizing a monomer component containing a monofunctional acrylicmonomer, and the monofunctional acrylic monomer is preferably at leastone selected from methacrylic acid or methacrylic acid alkyl ester.

As the acrylic resin, a copolymer obtained by polymerizing a monomercomponent containing methacrylic acid and methacrylic acid alkyl ester(namely, a copolymer containing a structural unit derived frommethacrylic acid and a structural unit derived from a methacrylic acidalkyl ester) is preferable. A copolymer of methacrylic acid and amethacrylic acid alkyl ester is more preferable for the acrylic resin ofthe third embodiment. A copolymer of methacrylic acid and methylmethacrylic acid (that is, methyl methacrylate) (hereinafter, thecopolymer may be referred to as “MMA-MAA copolymer”) is still morepreferable.

As more preferred embodiment of the acrylic resin of the thirdembodiment, there is exemplified a copolymer of methacrylic acid and amethacrylic acid alkyl ester in which the monofunctional acrylic monomerconsists of methacrylic acid and methacrylic acid alkyl ester, and anamount of methacrylic acid based on the total amount of methacrylic acidand methacrylic acid alkyl ester is from 0.1% by mass to 15% by mass(more preferably, 1% by mass to 15% by mass, still more preferably 5% bymass to 15% by mass).

As particularly preferred embodiment of the acrylic resin of the thirdembodiment, there is exemplified a MMA-MAA copolymer in which themonofunctional acrylic monomer consists of methacrylic acid and methylmethacrylate, and an amount of methacrylic acid based on the totalamount of methacrylic acid and methyl methacrylate is from 0.1% by massto 15% by mass (more preferably, 1% by mass to 15% by mass, still morepreferably 5% by mass to 15% by mass).

As compared to, for example, a polymethyl methacrylate (PMMA), thepreferred acrylic resin is advantageous in terms of the flexuralstrength of the material for a denture base and durability (yield pointstrength in a compression test) of a denture base made of the material.

The polymer component in the third embodiment may contain only one kindof acrylic resin or may contain two or more kinds of acrylic resin.

The polymer component in the third embodiment may contain a resin otherthan the acrylic resin.

Incidentally, a content of the acrylic resin in the material for adenture base in the third embodiment (when two or more kinds of acrylicresin are used, the content is a total content) based on a total amountof the material for a denture base is preferably 60% by mass or more,more preferably 80% by mass or more, still more preferably 90% by massor more, even more preferably 95% by mass or more, particularlypreferably 99% by mass or more.

(Rubber)

The polymer component in the third embodiment preferably contains arubber.

When the polymer component in the third embodiment contains a rubber, animpact strength of the material is further enhanced, and thus an impactdurability (a breaking weight in a falling ball test) of a denture baseformed of this material is further enhanced.

Examples and preferable examples of kinds of rubber are the same asdescribed in the first embodiment.

When the polymer component in the third embodiment contains a rubber,only one kind of rubber or two or more kinds of rubbers may be containedin the polymer component.

It is preferable that the rubber contains a graft polymer obtained bygraft polymerization of a rubbery polymer (preferably a rubbery polymerhaving a cross-linked structure) with a thermoplastic resin component.The preferable rubbery polymers and graft polymers are the same asdescribed in the first embodiment.

The rubber is preferably rubber particles.

When the polymer component in the third embodiment contains rubberparticles as the rubber, the rubber particles are dispersed in anacrylic resin. Therefore, the impact strength of the material for adenture base is further enhanced.

Examples and preferable examples of rubber particles are the same asdescribed in the first embodiment. Further, the properties such as acomposition or an average diameter are also the same as described in thefirst embodiment.

When the polymer component in the third embodiment contains a rubber,preferable content of the rubber based on the total amount of thematerial for a denture base is the same as described in the firstembodiment except the lower limit of content of the rubber.

The lower limit of the content of the rubber in the third embodiment ispreferably 1.5% by mass, more preferably 2% by mass.

In the material for a denture base of the third embodiment of theinvention, the flexural strength of 110 MPa or more, the maximum stressintensity factor 1.9 MPa·m^(1/2) or more, and the total work of fractureof 900 J/m² or more tend to be achieved by containing a copolymer ofmethacrylic acid and methacrylic acid alkyl ester (preferably a MMA-MAAcopolymer), and a rubber.

<Other Components>

The material for a denture base in the third embodiment may containother components, if necessary.

Examples of other components described in the first embodiment can beapplied to the third embodiment. Further, the preferable properties, thecontent or the effects of the other components of the first embodimentcan be also applied to the third embodiment.

In addition, the material for a denture base in the third embodimentpreferably contains a chain transfer agent.

The chain transfer agent the can be used in the third embodiment is notparticularly limited, and any chain transfer agent can be used.

Examples of the chain transfer agent include an alkylmercaptan such asn-octylmercaptan, n-dodecylmercaptan, t-dodecylmercaptan, 1,4-butanedithiol, 1, 6-hexamnedithiol, a aliphatic mercaptan; athioglycollic acid ester such as butanediol his (thioglycolate),hexanediol bis(thioglycolate); a mercaptopropionic acid ester such asethylene glycol bis(thiopropionate), butanediol bis(thiopropionate),trimethylolpropane tris (thiopropionate), pentaerythritoltetrakis(thiopropionate); terpinolene; a dimer of α-styrene.

One kind or two or more kinds of chain transfer agents may be used.

In the material for a denture base in the third embodiment, a content ofthe polymer component based on the total amount of the material for adenture base is preferably 90% by mass or more. When a rubber iscontained in the material, the content of the polymer component ispreferably from 90 to 99% by mass, more preferably from 92 to 98.5% bymass, particularly preferably from 92 to 98% by mass.

When the content of the polymer component is 90% by mass or more, theflexural strength of the material for a denture base of 110 MPa tends tobe achieved.

The size and the shape of the block body of the material for a denturebase of the third is not particularly limited as long as it is capableof obtaining a denture base by cutting. The preferable size and shape ofthe block body in the first embodiment can be applied to the thirdembodiment.

A method of manufacturing the material for a denture base in the thirdembodiment is not particularly limited. The method as described in thefirst embodiment can be applied to the third embodiment.

[Denture Base, Plate Denture]

The denture base of the present invention contains the material for adenture base of the invention.

Here, the “material for a denture base of the invention” means thematerial for a denture base in the first embodiment, the secondembodiment or the third embodiment (the same is applied to the followingdescription).

Accordingly, the denture base of the invention is excellent indurability (yield point strength).

The denture base of the present invention may be a denture base for fullremovable denture (so-called full denture) or a denture base for partialremovable denture (so-called partial denture).

Further, the denture base of the invention may be a denture base formaxillary denture (hereinafter also referred to as a “maxillary denturebase”), a denture base for submaxillary denture (hereinafter alsoreferred to as a “submaxillary denture base”), or a set of the maxillarydenture base and the submaxillary denture base.

In the denture base of the present invention, only a portion of thedenture base may be formed of the material for a denture base of theinvention, or the entire denture base may be formed of the material fora denture base of the invention.

Examples of the denture base in which only a portion thereof is formedof the material for a denture base of the invention include a denturebase in which at least a portion of a resin portion of the denture base(so-called metal base) including a metal portion and the resin portionis formed of the material for a denture base of the invention and adenture base in which only a portion of the denture base (so-calledresin base) including only a resin portion is formed of the material fora denture base of the invention.

Examples of the denture base entirely formed of the material for adenture base of the invention include a denture base including only aresin portion.

The denture base of the present invention is particularly preferably adenture base obtained by cutting a material for a denture base, which isa block body having a thickness of from 10 mm to 40 mm, as a preferredembodiment of the material for a denture base of the invention.

The plate denture of the present invention contains the denture base ofthe invention and artificial teeth fixed to the denture base.

Accordingly, the plate denture of the invention is excellent in thedurability (yield point strength) of the denture base.

The plate denture of the invention may be a partial removable denture ora full removable denture. Namely, the plate denture of the invention hasonly to contain at least one artificial tooth.

Further, the plate denture of the invention may be a maxillary denture,a submaxillary denture, or a set of the maxillary denture and thesubmaxillary denture.

The artificial tooth may be formed of an acrylic resin, for example.Examples of the acrylic resin are the same as described above. Theartificial tooth may further contain a filler and the like in additionto the acrylic resin.

FIG. 1 is a perspective view conceptually showing an example of theplate denture of the present invention.

As shown in FIG. 1, a maxillary denture 10 as an example of the platedenture of the invention is provided with a maxillary denture base 20 asan example of the denture base of the invention, an artificial tooth 12fixed to the maxillary denture base 20. In FIG. 1, only one ofartificial teeth is denoted with the reference numeral 12.

The maxillary denture base 20 is manufactured by cutting the materialfor a denture base of the invention. The maxillary denture 10 ismanufactured by fixing the artificial tooth 12 to the maxillary denturebase 20.

Although illustration is omitted, the denture base is separated into aplurality of portions, and only a portion thereof may be manufactured bycutting the material for a denture base of the present invention.

The denture base and the plate denture of the invention are not limitedto a denture base for maxillary denture and a plate denture formaxillary denture, respectively, and they may be naturally a denturebase for submaxillary denture and a plate denture for submaxillarydenture, respectively.

[Method of Manufacturing Denture Base, Method of Manufacturing PlateDenture]

The method of manufacturing a denture base of the present inventionincludes a cutting process of cutting a material for a denture base. Thematerial is preferably a block body having a thickness of from 10 mm to40 mm, as a preferred embodiment of the material for a denture base ofthe invention and thus obtaining a denture base.

In the cutting process, it is preferable to cut the material for adenture base which is the block body with the use of a CAD (ComputerAided Design)/CAM (Computer Aided Manufacturing) system to obtain adenture base.

Cutting using the CAD/CAM system can be performed using a CNC (ComputerNumerical Control) cutting machine in accordance with a cutting programcreated by CAD/CAM software.

The cutting program can be created by a well-known method based on athree-dimensional shape inside an oral cavity of a patient. When adenture base suitable for a patient has been already manufactured, thedenture base is optically scanned to obtain three-dimensional (3D) data,and a cutting program may be created based on the obtained 3D data.

In view of cutting a plurality of materials for a denture base at once,it is preferable that a changer device which can automatically exchangethe material for a denture base is provided adjacent to the CNC cuttingmachine.

The method of manufacturing a denture base of the present invention mayinclude processes other than the cutting process, if necessary. Examplesof other processes include a coloring process of coloring the denturebase.

The method of manufacturing a plate denture of the present inventionincludes a cutting process of cutting the material for a denture base ofthe invention to obtain a denture base and a fixing process of fixing anartificial tooth to the denture base.

The preferred embodiment of the cutting process is as described above.

In the fixing process, an artificial tooth can be fixed by a usualmethod using an adhesive. As the adhesive, a dental adhesive resincement “Super-Bond” (trademark) manufactured by Sun Medical Co., Ltd.may be used, for example.

Before an artificial tooth is fixed to a denture base with the use of anadhesive, well-known surface treatment (easy adhesion treatment) may bepreviously applied to a surface (adhesion surface) of at least one ofthe denture base and the artificial tooth.

The method of manufacturing a plate denture of the present invention mayinclude processes other than the cutting process and the fixing process,if necessary. Examples of other processes include a coloring process ofcoloring a denture base of the plate denture.

EXAMPLES

Hereinafter, although the embodiments of the present invention will bemore specifically described using examples, they are not limited to thefollowing examples unless they deviate from the spirit thereof.

Hereinafter, “wt %” is synonymous with % by mass.

Further, hereinafter, Examples 1A to 3A are examples of the material fora denture base in the embodiment A in the first embodiment, Examples 1Bto 6B are examples of the material for a denture base in the embodimentB in the first embodiment, Example 1C is an example of the material fora denture base in the embodiment C in the first embodiment, Examples 1Dto 3D are examples of the material for a denture base in the secondembodiment, and Examples 1E to 3E are examples of the material for adenture base in the third embodiment.

Example 1A

<Preparation of Test Piece for Flexural Test>

As the material for a denture base in the embodiment A in the firstembodiment, a resin block (“Kanase Lite” manufactured by KanaseIndustries, Co., Ltd.; the material was polymethylmethacrylate (PMMA);the shape is a rectangular solid shape having a size of 230 mm×190 mm×30mm) was provided, and the resin block was cut to obtain a rectangularsolid-shaped test piece for flexural test having a size of 80 mm×10 mm×4mm.

<Three-Point Flexural Test (Measurement of Flexural Strength andFlexural Modulus)>

The three-point test of the test piece for flexural test was conductedin accordance with JIS K7171 (2008) with the use of a 5-hook flexuraltest machine model 2001-5 manufactured by Intesco Co., Ltd. to measurethe flexural strength and the flexural modulus.

Here, the testing speed was 2 mm/min, and a length of the support spanwas 64 mm. The flexural modulus was calculated by a secant method

The result is shown in the following Table 1.

<Preparation of Test Piece for Impact Test>

A resin piece having the same size as the test piece for flexural testwas prepared by a similar method, and the resin piece was allowed tohave a notch having the shape A prescribed by JIS K7111-1 (2012) suchthat a remaining width was 8.0 mm, thus obtaining a test piece forimpact test (a single-notched test piece).

<Charpy Impact Test (Measurement of Impact Test)>

The Charpy impact test of the test piece for impact test was conductedunder the condition of edgewise impact in accordance with JIS K7111-1(2012) with the use of an impact tester DG-UB equipped with a constanttemperature bath manufactured by Toyo Seiki Seisaku-Sho Ltd., thusmeasuring the impact strength.

Further, in this test, after a pendulum hit the test piece, the swingangle (°) of the pendulum was measured. The swing angle shows that thesmaller the number, the larger energy absorption during hitting, thatis, that the impact resistance is excellent.

The above results are shown in the following Table 1.

<Weight Average Molecular Weight (Mw), Number Average Molecular Weight(Mn), and Molecular Weight Distribution (Mw/Mn) of Polymer Component>

In the polymer component (PMMA in Example 1A) in the resin block, theweight average molecular weight (Mw), the number average molecularweight (Mn), and the molecular weight distribution (Mw/Mn) were measuredin accordance with the above-described GPC measuring method.

The results are shown in the following Table 1.

<Manufacturing of Denture Base>

3D data of a maxillary denture base manufactured in Comparative Example1 to be described later was obtained using a 3D scanner.

A cutting program used for cutting the resin block (Kanase Lite) as amaterial for a denture base to obtain a maxillary denture base wascreated from the 3D data with the use of CAD/CAM software.

The resin block was cut using a CNC cutting machine in accordance withthe cutting program, thus obtaining a maxillary denture base.

<Compression Test of Denture Base (Measurement of Yield Point Strength)>

The compression test (measurement of the yield point strength) of themaxillary denture base was conducted using a universal material testingmachine AG-100kNX with a constant temperature bath manufactured byShimadzu Corporation.

More specifically, the maxillary denture base was placed on a test bedsuch that a mucosal surface (a surface which is in contact with aresidual ridge and a palate portion) was oriented upwardly. Then, acentral portion of the maxillary denture base was compressed at a speedof 1 mm/min by a bottom surface of a columnar rod having a diameter of20 mm (material: carbon steel S45C).

In the compression, displacement and strength were recorded, and amaximum point of the strength was determined, as the yield pointstrength.

The result is shown in the following Table 1.

<Evaluation of Cutting Workability of Material for Denture Base>

In the process from cutting of the resin block as a material for adenture base to acquisition of a denture base, the cutting workabilitywas evaluated based on the following evaluation criteria.

The result is shown in the following Table 1.

—Evaluation Criteria of Cutting Workability—

A: No cracking and chipping occurs during cutting, and the cuttingworkability was good.

B: At least one of cracking or chipping occurs during cutting, and thecutting workability was bad.

Example 2A

Similar operation to Example 1A was carried out, except that “KanaseLite” in Example 1A was changed to “CL-000” manufactured by Nitto JushiKogyo Co., Ltd., (resin block; the material was PMMA; the shape is arectangular solid shape having a size of 230 mm×190 mm×30 mm).

The results are shown in the following Table 1.

Example 3A

Similar operation to Example 1A was carried out, except that the testpiece for flexural test, the test piece for impact test, and the resinblock (Kanase Lite) in Example 1A were changed to a test piece forflexural test, a test piece for impact test, and a resin block producedas follows.

The results are shown in the following Table 1.

Preparation of Test Piece for Flexural Test (Production Example 1)

5.09 parts by mass of the A solution (obtained by adding 0.075 parts bymass of a white pigment, 0.013 parts by mass of a red pigment, and 0.002parts by mass of AIBN (2,2′-Azobis (isobutyronitrile); a polymerizationinitiator) to 5 parts by mass of a methyl methacrylate monomer to mixthe mixture under room temperature for homogenization) was added to 95parts by mass of a preporimerized methyl methacrylate syrup havingfluidity at room temperature. The obtained mixture was mixed under roomtemperature for homogenization and then defoamed. A defoamed compositionwas poured into a mold in which a gasket was interposed between twoinorganic glasses to be polymerized at 40° C. for 48 hours and 120° C.for 5 hours and, thus, to fabricate a rectangular solid-shaped resinblock having a thickness of 30 mm.

The resin block was cut to obtain a test piece for flexural test (thematerial was PMMA) having a size of 80 mm×10 mm×4 mm.

<Preparation of Test Piece for Impact Test>

A resin piece having the same size as the test piece for flexural testobtained as above was prepared by a similar method, and the resin piecewas allowed to have a notch having the shape A as in the test piece forimpact test in Example 1A and used as a test piece for impact test.

<Fabrication of Resin Block for Manufacturing Denture Base>

A resin block for manufacturing a denture base (having a size of 230mm×190 mm×30 mm) was fabricated by being cut out from the rectangularsolid-shaped resin block fabricated in the preparation of the test piecefor flexural test and having a thickness of 30 mm.

Example 1D

Similar operation to Example 1A was carried out, except that “KanaseLite” in Example 1A was changed to a resin block (“Natural Color”manufactured by Japan Extron Co., Ltd.; the shape is a rectangular solidshape having a thickness of 30 mm) formed of polysulfone (PSU) as thematerial for a denture base in the second embodiment.

The results are shown in the following Table 1.

Example 2D

Similar operation to Example 1A was carried out, except that “KanaseLite” in Example 1A was changed to a resin block (“Natural Color”manufactured by Japan Extron Co., Ltd.; the shape is a rectangular solidshape having a thickness of 30 mm) formed of polyether ether ketone(PEEK) as the material for a denture base in the second embodiment.

The results are shown in the following Table 1.

Comparative Example 1

Similar operation to Example 1A was carried out, except that the testpiece for flexural test, the test piece for impact test, and themaxillary denture base in Example 1A were changed to a test piece forflexural test, a test piece for impact test, and a maxillary denturebase produced as follows.

The results are shown in the following Table 2.

<Preparation of Test Piece for Flexural Test>

(Fabrication of Gypsum Mold for Test Piece for Flexural Test)

First, a flask for manufacturing a denture base (a set of a flask lowermold and a flask upper mold) was provided.

Then, a rectangular solid-shaped board having slightly large length,width, and thickness dimensions as compared to the size of 80 mm(length)×10 mm (width)×4 mm (thickness) was cut out from a resin block.A resin separating agent for a denture base, NEW ACROSEP (manufacturedby GC CO., LTD.) was applied onto the entire cut-out board.

Then, the flask lower mold was filled with gypsum dental plaster(manufactured by Noritake Co., Limited) mixed with a predeterminedamount of water and then left for a while. After the time when gypsumwas partially hardened, a central portion of gypsum was pressed to forma dent having a size large enough to make the hoard enter the dent.

After the gypsum was completely hardened, dental hard gypsum NewDiastone Natural Gray (manufactured by Morita Corporation) mixed with apredetermined amount of water was supplied into the dent and then leftfor a while. After the time when hard gypsum was partially hardened, theboard applied with the separating agent was embedded in the hard gypsumsuch that only an upper surface of the board was exposed, and a surfaceof the hard gypsum was smoothed.

After the hard gypsum was completely hardened, the separating agent wasapplied onto the entire surface of gypsum containing the hard gypsum.

Then, after the flask upper mold was attached above the flask lowermold, the hard gypsum New Diastone Natural Gray mixed with apredetermined amount of water was deposited so as to hide the board.

Then, the gypsum dental plaster mixed with a predetermined amount ofwater was supplied into a dental flask to the extent that the gypsumdental plaster overflows from the dental flask, and thereafter, thedental flask was lidded. After gypsum was hardened, the flask lower moldand the flask upper mold were separated to remove the board.

According to the above constitution, a gypsum mold for a test piece forflexural test (a set of an upper mold of a gypsum mold and a lower moldof a gypsum mold) was obtained in a flask for manufacturing a denture.

Here, the upper mold of a gypsum mold was fabricated in the flask uppermold, and the lower mold of a gypsum mold was fabricated in the flasklower mold. In the upper mold of a gypsum mold and the lower mold of agypsum mold, when these two molds are assembled with each other, a spacehaving the shape of the board is formed.

Then, the separating agent was applied onto the entire gypsum surface ofthe upper mold of a gypsum mold and the lower mold of a gypsum mold.

(Preparation of Test Piece for Flexural Test)

MMA was polymerized in a gypsum mold with the use of a flask formanufacturing a denture in which the gypsum mold for a test piece forflexural test was fabricated to obtain a board formed of PMMA and, thus,to polish the obtained board, thereby preparing a test piece forflexural test having a size of 80 mm×10 mm×4 mm. The detailed operationis as follows.

First, a resin material for a denture base, Acron Clear No. 5(manufacture by GC CO., LTD.) was provided, and 6 g of a powder materialand 2.5 g of a liquid material thereof were weighed into a container andthen mixed with each other. When the obtained mixture was left for awhile to be changed to a rice cake-like state, a generous amount of therice cake-like mixture was put on a dent of a lower mold of a gypsummold fabricated in a flask lower mold, and the shape was arranged.

Then, a flask upper mold in which an upper mold of a gypsum mold wasfabricated was put on the flask lower mold, and pressure was applied bya pressing machine. Then, the flask upper mold was removed, a ricecake-like resin material for a denture base protruding from the dent wasremoved. The flask upper mold was put on the flask lower mold again, andpressure was applied by the pressing machine. After that, the flask (inwhich the flask upper mold and the flask lower mold are assembled witheach other) was fixed by a flask clamp.

This flask was put into a pan containing water to be slowly heated to100° C. for 30 minutes or more by a gas range. The flask was heated for30 to 40 minutes after reaching 100° C., and then heating was terminatedto cool the flask to 30° C.

Subsequently, the flask lower mold and the flask upper mold wereseparated, and the gypsum mold was then broken to take out a finishedboard (formed of PMMA). The taken out board was polished to obtain arectangular solid-shaped board having a size of 80 mm×10 mm×4 mm, andthis board was used as a test piece for flexural test (formed of PMMA).

<Preparation of Test Piece for Impact Test>

A resin piece having the same size as the test piece for flexural testobtained as above was prepared by a similar method, and the resin piecewas allowed to have a notch having the shape A as in the test piece forimpact test in Example 1A and used as a test piece for impact test.

<Manufacturing of Denture Base>

(Manufacturing of Wax Denture)

Primary impressions of the upper jaw and the lower jaw of a patient weretaken, and a tray having a shape suitable for the patient was fabricatedbased on the primary impressions. The precision impression of thepatient was taken using the obtained tray. A gypsum model which has ashape suitable for the patient and in which upper and lower portions areseparately provided was fabricated based on the taken precisionimpression.

Then, the upper and lower portions of the gypsum model are combined witheach other to fabricate a biteplate used for reproducing occlusion ofthe upper and lower jaws and formed of a base plate and wax.

Then, a state of jaw movement was observed while watching the oralcavity of the patient, the jaw movement was reproduced by the biteplateto three-dimensionally acquire an occlusion state and, thus, todetermine an occlusion position, thereby preparing a wax denture base (aset of a maxillary denture and a submaxillary denture).

Artificial teeth, to that a wax pattern separating agent (manufacturedby Shofu Inc.) had been applied in advance, were arranged on theresulted wax denture base, and try-in and adjustment were done tocomplete a wax denture (a set of a maxillary denture and a submaxillarydenture).

(Preparation of Gypsum Mold for Denture Base)

First, a flask for manufacturing a denture constituted of a flask lowermold and a flask upper mold was provided.

Further, artificial teeth were removed from the wax denture to provide awax denture base.

Then, the wax denture base and the above-described gypsum model werecombined with each other, and they were put into the flask lower mold asthey were. The flask lower mold was filled with gypsum dental plastermixed with a predetermined amount of water and then left for a while.After gypsum was hardened, the above-described separating agent wasdropped on gypsum to be applied over the entire surface with the use ofa brush. After that, the flask upper mold was put on the flask lowermold, and gypsum was supplied therein fully to the frame. The mold waslidded to be left until the gypsum was completely hardened.

After the gypsum was hardened, the flask upper mold and the flask lowermold were separated to be heated with hot water and, thus, to melt outwax, to remove a base plate.

According to the above constitution, a gypsum mold for a denture baseconstituted of an upper mold of a gypsum mold and a lower mold of agypsum mold was obtained.

Here, the upper mold of a gypsum mold was fabricated in the flask uppermold, and the lower mold of a gypsum mold was fabricated in the flasklower mold. In the upper mold of a gypsum mold and the lower mold of agypsum mold, when these two molds are assembled with each other, a spacehaving the shape of the wax denture base is formed.

Then, the separating agent was applied onto the entire gypsum surface ofthe upper mold of a gypsum mold and the lower mold of a gypsum mold.

(Manufacturing of Denture Base)

In the preparation of a test piece for flexural test in ComparativeExample 1, a denture base (a set of a maxillary denture base and asubmaxillary denture base; each material was PMMA) was obtainedsimilarly to the preparation of the test piece for flexural test, exceptthat a gypsum mold for a test piece for flexural test was changed to theabove-described gypsum mold for a denture base.

Of them, the maxillary denture base was used in a compression test(measurement of the yield point strength),

Comparative Examples 2 to 6

Similar operation to Comparative Example 1 was carried out, as shown inthe following Table 2, except that Acron Clear No. 5 (manufactured by GCCO., LID.) in Comparative Example 1 was changed to Acron Live Pink No. 3(manufactured by GC CO., LTD.), Acron Live Pink No. 8 (manufactured byGC CO., LTD.), Paraexpress Ultra Clear No. 7 (manufactured by HeraeusKulzer GmbH.), Paraexpress Ultra Pink No. 1 (manufactured by HeraeusKulzer GmbH.), or Paraexpress Ultra Pink Live No. 34 (manufactured byHeraeus Kulzer GmbH.). In each example, the material for a denture baseand the denture base are formed of PMMA.

The results are shown in the following Table 2.

TABLE 1 Example 1A Example 2A Example 3A Example 1D Example 2D Materialfor Material PMMA PMMA PMMA PSU PEEK denture Brand or manufacturingmethod Kanase Lite CL-000 Production Example 1 Natural Color NaturalColor base Three-point Flexural strength 121 127 124 122 188 flexuraltest [MPa] Flexural 2941 3137 3120 2533 3120 modulus [MPa] Charpy impactImpact strength 1.41 1.47 1.52 3.25 3.5 test [kJ/m²] Angle [°] 132 133132 118 126 Molecular Mw 4,550,000 4,950,000 4,230,000 N.D. N.D. weightMn 1,150,000 1,750,000 850,000 N.D. N.D. Mw/Mn 4.0 2.8 5.0 N.D. N.D.Cutting workability A A A A A Method of manufacturing denture baseCutting Cutting Cutting Cutting Cutting Evaluation Compression Yieldpoint 1.5 1.8 1.9 3.0 3.9 of denture test strength [kN] base

TABLE 2 Comparative Comparative Comparative Comparative ComparativeComparative Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Material for Material PMMA PMMA PMMA PMMA PMMA PMMA denture base Brandor manufacturing method Acron clear Acron pink Acron live pinkParaexpress Paraexpress Paraexpress No. 5 No. 3 No. 8 ultra clear ultrapink ultra pink live No. 7 No. 1 No. 34 Three-point Flexural 99 95 79 8379 77 flexural test strength [MPa] Flexural 2858 2590 2880 2900 26402840 modulus [MPa] Charpy impact test Impact 1.57 1.53 1.41 1.24 1.241.24 strength [kJ/m²] Angle [°] 132 133 134 135 135 135 Molecular weightMw 1,150,000 N.D. 1,120,000 270,000 N.D. 260,000 Mn 320,000 N.D. 320,000100,000 N.D. 100,000 Mw/Mn 3.6 N.D. 3.5 2.8 N.D. 2.6 Cutting workability— — — — — — Method of manufacturing denture base Polymerization afterputting into mold Evaluation of Compression test Yield point 1.1 1.0 1.01.1 0.9 1.1 denture base strength [kN]

—Description of Table 1 and Table 2—

“N. D.” means “No Data” (this similarly applies to Table 3 andsubsequent Tables).

“Angle” in the Charpy impact test indicates a swing angle)(° of apendulum after the pendulum hits a test piece (this similarly applies toTable 3 and subsequent Tables).

As shown in Table 1 and Table 2, the denture bases manufactured by usingthe materials for a denture base in Examples 1A to 3A corresponding tothe material for a denture base in the embodiment A in the firstembodiment and the materials for a denture base in Examples 1D and 2Dcorresponding to the material for a denture base in the secondembodiment were all excellent in the durability (yield point strength).In addition, those materials for a denture base were excellent in thecutting workability.

Meanwhile, in the denture bases in Comparative Examples 1 to 6manufactured by using the material for a denture base in which the Mw ofthe contained polymer component (PMMA) was less than 120, the durability(yield point strength) was low.

As seen in Table 1 and Table 2, when the flexural strength of thematerial for a denture base is 100 MPa or more (particularly, 110 MPa ormore), the yield point strength in the compression test in a denturebase formed of this material is significantly enhanced.

Further, as seen in Table 1, in the material for a denture base inExample 1D, the yield point strength is high although the flexuralmodulus is 2533 MPa. Meanwhile, as seen in Table 2, in ComparativeExamples 1 to 6, the yield point strength is low although the flexuralmodulus is 2590 MPa or more. These show that even if the flexuralmodulus is high, there is the case in which the yield point strength ofa denture base is low.

Furthermore, in any of the materials for a denture base in Examples 1Dand 2D, since the Charpy impact strength is high, it is expected thatthe impact resistance of denture bases to be obtained is high.

Example 1B

A resin block corresponding to the material for a denture base in theembodiment B of the first embodiment was fabricated. The details are asfollows.

First, 2 parts by mass of MUX-60 (manufactured by UMG ABS, Ltd.) as arubber, 0.002 parts by mass of AIBN (2,2′-Azobis (isobutyronitrile); apolymerization initiator), and 48 parts by mass of methyl methacrylatewere mixed under room temperature to obtain a dispersion dispersed withthe rubber.

This dispersion was added to 50 parts by mass of a preporimerized methylmethacrylate syrup having fluidity at room temperature and then mixedunder room temperature for homogenization.

The homogenized composition was defoamed, and the defoamed compositionwas poured into a mold in which a gasket is interposed between twoinorganic glasses to be polymerized at 40° C. for 48 hours and 120° C.for 5 hours and, thus, to fabricate a rectangular solid-shaped resinblock (material for a denture base) having a thickness of 30 mm.

Here, MUX-60 (manufactured by UMG ABS, Ltd.) is a rubber obtained bygraft polymerization of a butadiene (co)polymer, which is a rubberypolymer having a cross-linked structure, with a thermoplastic resincomponent.

Further, the obtained resin block is a resin block formed of a polymercomponent which is a mixture of PMMA and the rubber (MUX-60).

Similar operation to Example 1A was carried out, except that “KanaseLite” in Example 1A was changed to the above-described resin block.

The results are shown in the following Table 3.

Example 2B

Similar operation to Example 1B was carried out, except that the amountof MUX-60 (manufactured by UMG ABS, Ltd.) was changed to 4 parts bymass, and the amount of methyl methacrylate was changed to 46 parts bymass.

The results are shown in the following Table 3.

Example 3B

Similar operation to Example 1B was carried out, except that the amountof MUX-60 (manufactured by UMG ABS, Ltd.) was changed to 6 parts bymass, and the amount of methyl methacrylate was changed to 44 parts bymass.

The results are shown in the following Table 3.

TABLE 3 Example 1B Example 2B Example 3B Material for Material PMMA +PMMA + PMMA + denture base rubber rubber rubber Brand or manufacturingmethod Add 2 wt % Add 4 wt % Add 6 wt % of MUX-60 of MUX-60 of MUX-60Three-point Flexural strength [MPa] 115 109 103 flexural test Flexuralmodulus [MPa] 2922 2785 2775 Charpy impact Impact strength [kJ/m²] 2.562.79 4.42 test Angle [°] 122.2 119.9 107.6 Molecular Mw 3,040,0003,650,000 3,000,000 weight Mn 580,000 780,000 630,000 Mw/Mn 5.3 4.7 4.8Cutting workability A A A Method of manufacturing denture base CuttingCutting Cutting Evaluation of Compression Yield point strength [kN] 1.72.3 2.0 denture base test

—Description of Table 3—

MUX-60 is a rubber obtained by graft polymerization of a butadiene(co)polymer, which is a rubbery polymer having a cross-linked structure,with a thermoplastic resin component.

As shown in Table 3, the denture bases manufactured by using thematerials for a denture base in Examples 1B to 3B corresponding to theembodiment B in the first embodiment were all excellent in thedurability (yield point strength) as compared to the above-describeddenture bases in Comparative Examples 1 to 6 (Table 2). In addition, thematerials for a denture base in Examples 1B to 3B were excellent in thecutting workability.

Further, in the materials for a denture base in Examples 19 to 3B, sincethe Charpy impact strength is high, it is expected that the impactresistance of denture bases to be obtained is high.

Example 1C

A resin block corresponding to the material for a denture base in theembodiment C of the first embodiment was fabricated. The details are asfollows.

Similar operation to Production Example 1 in Example 3A was carried out,except that the amount of a methyl methacrylate syrup was changed to 90parts by mass, and 5 parts by mass of a methyl methacrylate monomer waschanged to 10 parts by mass of methacrylic acid, and a rectangularsolid-shaped resin block having a thickness of 30 mm was fabricated. Thematerial of the obtained resin block is a methylmethacrylate-methacrylic acid copolymer (hereinafter referred to as“MMA-MAA copolymer”).

Similar operation to Example 1A was carried out, except that “KanaseLite” in Example 1A was changed to the above-described resin block.

The results are shown in the following Table 4.

Example 4B

Similar operation to Example 2B was carried out, except that “MUX-60” inExample 2B was changed to “M-521” having the same mass.

Here, “M-521” is “KANE ACE (trademark) M-521” manufactured by Kaneka.Corporation and is a rubber obtained by graft polymerization of abutadiene (co)polymer, which is a rubbery polymer having a cross-linkedstructure, with a thermoplastic resin component.

The results are shown in the following Table 4.

Example 5B

Similar operation to Example 2B was carried out, except that “MUX-60” inExample 2B was changed to “W-450” having the same mass.

Here, “W-450” is “Metablen (trademark) W-450” manufactured by MitsubishiRayon Co., Ltd. and is a rubber obtained by graft polymerization of anacrylic (co)polymer, which is a rubbery polymer having a cross-linkedstructure, with a thermoplastic resin component.

The results are shown in the following Table 4.

Example 6B

Similar operation to Example 2B was carried out, except that “MUX-60” inExample 2B was changed to “S-2001” having the same mass.

Here, “S-2001” is “Metablen (trademark) S-2001” manufactured byMitsubishi Rayon Co., Ltd. and is a rubber obtained by graftpolymerization of a silicone-based polymer with a thermoplastic resincomponent.

The results are shown in the following Table 4.

Example 3D

Similar operation to Example 1A was carried out, except that “KinaseLite” in Example 1A was changed to a resin block (“Radel R5000”manufactured by Solvay Specialty Polymers Japan Co., Ltd.; the shape wasa rectangular solid shape having a thickness of 30 mm) formed ofpolyphenyl sulfone (PPSU) which was the material for a denture base inthe second embodiment.

The results are shown in the following Table 4.

Comparative Example 7

A resin block was fabricated as follows, using Acron Clear No. 5(manufactured by GC CO., LTD) as a raw material.

60 parts by mass of the powder material of Acron Clear No. 5 and 25parts by mass of the liquid material thereof were weighed into acontainer and then mixed with each other. When the obtained mixture wasleft for a while to be changed to a rice cake-like state, the ricecake-like mixture was supplied into a previously provided acrylic mold(having a rectangular solid shape having an inner size of 120 mm×130mm×35 mm) in which a polyolefin film was placed inside, and the mold waslidded. Subsequently, after this mold was put into an autoclavecontaining water, the inside of the autoclave was pressurized. Thepressurized autoclave was slowly heated to 100° C. for 60 minutes ormore. Heating was continued after the temperature of the autoclavereached 100° C., and the temperature of the autoclave was maintained at100° C. for 30 to 40 minutes. Subsequently, heating of the autoclave wasterminated, and the autoclave was cooled to 30° C.

Then, the pressure inside the autoclave was returned to normal pressure.The mold was taken out from the autoclave, and a finished block wastaken out from the mold. The block was polished to obtain a rectangularsolid-shaped resin block having a size of 110 mm×120 mm×30 mm.

Then, similar operation to Example 1A was carried out, except that“Kanase Lite” in Example 1A was changed to the above-described resinblock. However, the three-point flexural test and the Charpy impact testwere omitted.

The results are shown in the following Table 4.

Comparative Example 8

Similar operation to Comparative Example 7 was carried out, except thatAcron Clear No. 5 (manufactured by GC CO., LTD.) in Comparative Example7 was changed to Acron Live Pink No. 8 (manufactured by GC CO., LTD.).

The results are shown in the following Table 4.

TABLE 4 Comparative Comparative Example 1C Example 4B Example 5B Example6B Example 3D Example 7 Example 8 Material Material MMA-MAA PMMA +PMMA + PMMA + PPSU PMMA PMMA for copolymer rubber rubber rubber dentureBrand or manufacturing MMA-MAA Add 4 wt % Add 4 wt % Add 4 wt % RadelR5000 Acron Clear Acron Live Pink base method copolymer of M-521 ofM-450 of S-2001 No. 5 No. 8 (MAA 10 wt %) Three-point Flexural 139 104103 105 111 N.D. N.D. flexural test strength [MPa] Flexural 3585 27222755 2784 2168 N.D. N.D. modulus [MPa] Charpy Impact 1.51 4.40 2.73 3.1610.79 N.D. N.D. impact test strength [kJ/m²] Angle [°] 132 109 122 11863 N.D. N.D. Molecular Mw 1,220,000 4,540,000 4,410,000 4,610,000 N.D.990,000 1,000,000 weight Mn 230,000 710,000 290,000 340,000 N.D. 160,000170,000 Mw/Mn 5.4 6.4 15 14 N.D. 6.3 6.0 Cutting workability A A A A A BB Method of manufacturing denture base Cutting Cutting Cutting CuttingCutting Cutting Cutting Cutting Evaluation Compression Yield point 2.72.5 1.4 2.5 2.5 1.2 1.0 of test strength denture [kN] base

—Description of Table 4—

M-521 is a rubber obtained by graft polymerization of a butadiene(co)polymer with a thermoplastic resin component.

W-450 is a rubber obtained by graft polymerization of an acrylic(co)polymer with a thermoplastic resin component.

S-2001 is a rubber obtained by graft polymerization of a silicone-basedpolymer with a thermoplastic resin component.

As shown in Table 4, the denture bases manufactured by using thematerials for a denture base in the respective Examples were allexcellent in the durability (yield point strength) as compared to thedenture bases in Comparative Examples 1 to 8 (Comparative Examples 1 to6 are shown in Table 2). In addition, the materials for a denture basein the respective Examples were excellent in the cutting workability.Among the respective Examples, the denture bases in Examples 1C, 4B, 6B,and 3D were particularly excellent in the durability (yield pointstrength).

As compared to each Example, in the denture bases manufactured by usingthe materials for a denture base in Comparative Examples 7 and 8 havingthe Mw of less than 120 and formed of PMMA, the durability (yield pointstrength) was low. Further, as compared to the material for a denturebase in each Example, the materials for a denture base in ComparativeExamples 7 and 8 were inferior in the cutting workability (namely, atleast one of cracking and chipping occurs during cutting).

Reference Example 1

As Reference Example 1, based on a denture base, there is shown anexample of a method of estimating the flexural strength of a materialfor a denture base used as a raw material of the denture base.

It is practically difficult to cut out a test piece having a length of80 mm, a width of 10 mm, and a thickness of 4 mm from the denture base.

However, when a minute flexural test of the denture base is conducted asfollows, the flexural strength of the material for a denture base usedas a raw material of the denture base can be estimated.

—Minute Flexural Test—

A minute test piece having a length of 25 mm, a width of 2 mm, and athickness of 2 mm was cut out from a denture base, and a three-pointflexural test of the obtained minute test piece was conducted under theconditions of a testing speed of 1 mm/min and a length of the supportspan of 20 mm. This three-point flexural test is referred to as the“minute flexural test”, and the obtained flexural strength is referredto as “minute flexural strength”.

Among the measurement conditions of the “minute flexural test”,conditions other than the above conditions are similar to the conditionsin the three-point flexural test of the material for a denture base.

Regarding the denture bases in Examples 1A, 1B, 2B, 3B, 1D, and 2D, theminute flexural strength was measured.

The obtained results are shown in the following Table 5.

The following Table 5 also shows the flexural strength of the materialfor a denture base in each Example.

TABLE 5 Minute flexural strength Flexural strength of material ofdenture base [MPa] for denture base [MPa] Example 1A 116 121 Example 1B108 115 Example 2B 102 109 Example 3B 95 103 Example 1D 115 122 Example2D 165 188

FIG. 2 is a graph showing a relationship between the minute flexuralstrength of the denture base and the flexural strength of the materialfor a denture base and created based on the results of Table 5.

As seen in FIG. 2, the flexural strength of the material for a denturebase is directly proportional to the minute flexural strength of thedenture base. Accordingly, it is found that the flexural strength of thematerial for a denture base used as a raw material of the denture basecan be estimated by measuring the minute flexural strength of thedenture base.

It is assumed from the graph of FIG. 2 that for example, a denture basehaving a minute flexural strength of 95 MPa or more is manufacturedusing, as a raw material, a material for a denture base having flexuralstrength of 100 MPa or more. It is expected that the denture base havinga minute flexural strength of 95 MPa or more is a denture base excellentin the durability (yield point strength in a compression test).

Reference Example 2

As Reference Example 2, based on a denture base, there is shown anexample of a method of estimating the impact strength (Charpy impactstrength) of a material for a denture base used as a raw material of thedenture base.

It is practically difficult to cut out a single-notched test piecehaving a length of 80 mm, a width of 10 mm, a remaining width of 8 mm,and a thickness of 4 mm from the demure base.

However, when a minute impact test of the denture base is conducted asfollows, the impact strength (Charpy impact strength) of the materialfor a denture base used as a raw material of the denture base can beestimated.

—Minute Impact Test—

A minute test piece having a length of 25 mm, a width of 2 mm, and athickness of 2 mm was cut out from a denture base. A Dynstat impact testof the obtained minute test piece was conducted using a new Dynstattester manufactured by Toyo Seiki Seisaku-Sho Ltd. under the conditionsof a hitting direction in flatwise verticality, hammer energy: 20 kg·cm,swing angle: 90°, elevated angle: 90°, and unnotched, such that theminute test piece was hit at a position of 7.5 mm above a lower end ofthe minute test piece.

The Dynstat impact test is referred to as the “minute impact test”, andthe obtained impact strength is referred to as the “minute impactstrength”.

Regarding the denture bases in Examples 3A, 1B, 2B, and 3B, the minuteimpact strength was measured.

The obtained results are shown in the following Table 6.

The following Table 6 also shows the impact strength of the material fora denture base in each Example.

TABLE 6 Minute impact strength of Impact strength of material denturebase [kJ/m²] for denture base [kJ/m²] Example 3A 10.1 1.52 Example 1B14.7 2.56 Example 2B 34.5 2.79 Example 3B 38.8 4.42

FIG. 3 is a graph showing a relationship between the minute impactstrength of the denture base and the impact strength of the material fora denture base and created based on the results of Table 6.

As seen in FIG. 3, the impact strength of the material for a denturebase is directly proportional to the minute impact strength of thedenture base. Accordingly, it is found that the impact strength of thematerial for a denture base used as a raw material of the denture basecan be estimated by measuring the minute impact strength of the denturebase.

It is assumed from the graph of FIG. 3 that for example, a denture basehaving minute impact strength of 13 kJ/m² or more is manufactured using,as a raw material, a material for a denture base having impact strengthof 2.0 kJ/m² or more. It is expected that the denture base having aminute impact strength of 13 kJ/m² or more is a denture base excellentin the impact resistance.

Example 1E

<Preparation of Material for Denture Base>

A material for denture base was prepared as follows.

7.032 parts by mass of Liquid A [that is a liquid in which 2 parts bymass of MUX-60 (that is a rubber, manufactured by UMG ABS, LTD), 0.03parts by mass of terpinolene (that is a chain transfer agent,manufactured by Tokyo Chemical Industry Co., Ltd.), and 0.002 parts bymass of AIBN (2,2′-Azobis(isobutyronitrile, that is a polymerizationinitiator) were added to 5 parts by mass of methacrylic acid monomer,and then mixed at room temperature to homogenize] was added to 93 partsby mass of prepolymerized methyl methacrylate syrup having a fluidity atroom temperature, and then mixed at room temperature to homogenize,followed by defoaming. The defoamed composition was poured into a moldin which a gasket was interposed between two inorganic glass plates tobe polymerized at 40° C. for 48 hours, and further polymerized at 120°C. for 5 hours, to fabricate a rectangular solid-shaped resin block (amaterial for a denture base) having a thickness of 30 mm.

MUX-60 (manufactured by UMG ABS, Ltd.) is a rubber obtained by graftpolymerization of a butadiene (co)polymer, which is a rubbery polymerhaving a cross-linked structure, with a thermoplastic resin component.

A material of the obtained resin block is a mixture of MMA-MAA copolymerand the rubber (MUX-60).

The three-point flexural test, the Charpy impact test, the compressiontest of a denture base, and the evaluation for cutting workability ofthe material for a denture base were performed as described in Example1A except that the resin block of Example 1E was used.

The results are shown in the following Table 7.

<Preparation of Test Piece for Fracture Toughness Test>

The resin block was cut to obtain a piece of the resin having a size of39 mm long, 8 mm height and 4 mm wide, and the resin piece was allowedto have a notch prescribed by JIS T6501 (2012), thus obtaining a testpiece for fracture toughness test (a notched test piece).

<Fracture Toughness Test (Measurement of Maximum Stress Intensity Factorand Total Work of Fracture>

The fracture toughness test by a flexural test of the test piece wasconducted in accordance with JIS T6501 (2012) with the use of auniversal test machine (model: 210X), manufactured by Intesco Co., Ltd.to measure a maximum stress intensity factor and a total work offracture. The testing speed was 1 mm/min, and a length of the supportspan was 32 mm. The flexural modulus was calculated by a secant method

The result is shown in the following Table 7.

<Weight Average Molecular Weight (Mw), Number Average Molecular Weight(Mn), and Molecular Weight Distribution (Mw/Mn) of Polymer Component>

In the polymer component (MMA-MAA copolymer in Example 1E) in the resinblock, the weight average molecular weight (Mw), the number averagemolecular weight (Mn), and the molecular weight distribution (Mw/Mn)were measured in accordance with the above described GPC measuringmethod.

The results are shown in the following Table 7.

A maxillary denture base for compression test was prepared and acompression test of the denture base was carried out as described inExample 1A.

<Manufacturing of Denture Base for Falling Ball Test>

Thinning 3D data, in which a thickness of a portion of the palate ofupper jaw is 1.2 mm thinner compared to that of 3D data of a maxillarydenture base manufactured for the compression test, was obtained using a3D scanner.

A cutting program for cutting the resin block as a material for adenture base to obtain a maxillary denture base was created from the 3Ddata with the use of CAD/CAM software.

The resin block was cut using a CNC cutting machine in accordance withthe cutting program, thus obtaining a thinning maxillary denture base.

<Falling Ball Test of Denture Base (Measurement of a Breaking Weight)>

Falling ball test (that is, measurement of a breaking weight) of thethinning maxillary denture base was carried out.

More specifically, the thinning maxillary denture base was placed on atest bed such that a mucosal surface (a surface which is in contact witha residual ridge and a palate portion) was oriented upwardly. Then,steel balls having different weight were dropped from 100 cm height onthe thinning maxillary denture base in increasing order by weight so asto the ball impacts a center portion of the denture base. The weight ofa ball, that firstly breaks the denture base, was determined as abreaking weight.

The weight of the steel balls were 6.9 g, 8.4 g, 9.0 g, 10.0 g, 11.2 g,11.9 g, 13.8 g, 14.0 g, 16.3 g, 16.7 g, 18.9 g, 20.0 g, 21.7 g, 23.8 g,24.8 g, 28.0 g, 28.0 g, 33.2 g, and 45.5 g, respectively.

The results are shown in the following Table 7.

Example 2E

Similar operation to Example 1E was carried out, except that the amountof methyl methacrylate syrup and methacrylic acid monomer were changedto 88 parts by mass and 10 parts by mass respectively, to fabricate arectangular solid shape resin block having a thickness of 30 mm (amaterial for denture base).

The material of the obtained resin block is a mixture of a copolymer ofmethyl methacrylate and methacrylic acid (MMA-MAA copolymer) and arubber (MUX-60).

Example 3E

Similar operation to Example 1E was carried out, except that 2 parts bymass of MUX-60 was changed to 2 parts by mass of KANEACE (trademark)M-521 (that is a rubber, manufactured by Kaneka. Corporation) tofabricate a rectangular solid shape resin block having a thickness of 30mm (a material for denture base).

“M-521” is a rubber obtained by graft polymerization of a butadiene(co)polymer, which is a rubbery polymer having a cross-linked structure,with a thermoplastic resin component.

The material of the obtained resin block is a mixture of a copolymer ofmethyl methacrylate and methacrylic acid (MMA-MAA copolymer) and arubber (M-521).

Comparative Example 9

Similar operation to Comparative Example 1 was carried out, except thatAcron Clear No. 5 (manufactured by GC CO., LTD.) was changed to LuxonLive Pink No. 8 (manufactured by GC CO., LTD.). A mixture ratio of thepowder and the liquid (powder material/liquid material) in Luxon LivePink No. 8 was 100/50 (g/mL). Luxon Live Pink No. 8 is a PMMA resin fora denture base that satisfies the additional prescribed properties foran impact resistant material (that is, maximum stress intensity factorand total work of fracture) in accordance with JIS T6501. Namely, thematerial of the material for a denture base and the denture plate is aPMMA resin.

The results are shown in the following Table 7.

In addition, a falling ball test was conducted on Comparative Example 9using the material for a denture base and the thinning denture base forfalling ball test (thinning maxillary denture base) prepared as follows.

<Preparation of Material for Denture Base>

A resin block was prepared as described in Example 1E, and then athrough hole, which is a slightly larger than the denture base to beprepared for falling ball test, was provided on the center part of theresin block. The obtained resin block was placed on an iron plate with asmooth surface that is slightly larger than the resin block.

A powder material and a liquid material of Luxon Live Pink No. 8 wasmeasured in a container, and then the materials were mixed in a ratio of100/50 (powder material/liquid material). The mixture left to stand fora while to form a dough. The through hole of the resin block on the ironplate was filled with the dough, and then another iron plate with thesame size to the iron plate was placed on top of the resin block andapplied a pressure to the iron plates using a press machine. The resinblock was fixed with clamps.

The fixed resin block was placed in a pot filled with water, and washeated slowly up to 100° C. over 1 hour, and further heated for 30 to 40minutes after reaching the temperature of 100° C. then heating wasstopped and cooled to 30° C.

Subsequently, the clamps and the plates were removed, and a rectangularsolid shape resin block having a thickness of 30 mm (a material fordenture base), in which the through hole on the center part of the resinblock is filled with a cured material of Luxon Live Pink No. 8, wasobtained.

<Preparation of Denture Base for Falling Ball Test>

A thinning maxillary denture base was obtained by cutting the resinblock in accordance with the cutting program based on the thinning 3Ddata prepared in Example 1E.

<Falling Ball Test of Denture Base (Measurement of a Breaking Weight)>

A falling ball test of the thinning maxillary denture base (measurementof a breaking weight) was conducted in a similar matter to Example 1E.

The results are shown in the following Table 7.

Comparative Example 101

Similar operation to Compared Example 1 was carried out, except thatAcron Clear No. 5 (manufactured by GC CO., LTD.) was changed toProimpact Live Pink No. 8 (manufactured by GC CO., LTD.). A mixtureratio of the powder and the liquid (powder material/liquid material) inProimpact Live Pink No. 8 was 100/50 (g/mL). Proimpact Live Pink No, 8is a PMMA resin for a denture base that satisfies the additionalprescribed properties for an impact resistant material (that is, maximumstress intensity factor total work of fracture) in accordance with JIST6501. Namely, the material for a denture base and the denture plate isa PMMA resin.

The results are shown in the following Table 7.

<Fracture Toughness Test>

Fracture toughness test was carried out as described in Example 1E,except that the resin blocks, which are the materials, obtained inComparative Examples 1, 3, 6, 9 and 10 were used.

The results are shown in the following Table 7.

TABLE 7 Comparative Comparative Comparative Comparative ComparativeExample 1 Example 3 Example 6 Example 9 Example 10 Material MaterialPMMA PMMA PMMA PMMA PMMA for Brand or manufacturing Acron clear Acronlive Paraexpress Luxon live Proimpact denture method No. 5 pink No. 8Ultra Pink pink No. 8 live pink base Live No. 34 No. 8 Three-pointFlexural 99 79 77 95 72 flexural test strength [MPa] Flexural 2858 28802840 2627 1985 modulus [MPa] Charpy Impact 1.57 1.41 1.24 2.64 5.73impact test strength [kJ/m²] Angle [°] 132 134 135 121 98 FractureMaximum 1.37 1.53 1.45 2.19 2.24 toughness stress intensity test factor[MPa · m^(1/2)] Total work of 244 274 258 1080 2350 fracture [J/m²]Molecular Mw 1,150,000 1,120,000 260,000 230,000 620,000 weight Mn320,000 320,000 100,000 110,000 200,000 Mw/Mn 3.6 3.5 2.6 2.2 3.1Cutting workability — — — — — Denture Compression ManufacturingPolymerization after putting into mold base test method of denture baseYield point 1.1 1.0 1.1 1.6 1.8 strength [kN] Falling ball Manufacturing— — — Cutting — test method of denture base Breaking — — — 11.2 — weight[g] Example 1E Example 2E Example 3E Material Material MMA-MAA MMA-MAAMMA-MAA for (copolymer) + (copolymer) + (copolymer) + denture rubberrubber rubber base Brand or manufacturing 5.0 wt % of 10.0 wt % of 5.0wt % of method MMA and MMA and MMA and 2.0 wt % of 2.0 wt % of 2.0 wt %of MUX-60 MUX-60 M-521 were were added were added added Three-pointFlexural 122 122 115 flexural test strength [MPa] Flexural 3248 32453162 modulus [MPa] Charpy Impact 2.73 2.81 2.90 impact test strength[kJ/m²] Angle [°] 121 121 120 Fracture Maximum 2.64 2.67 2.49 toughnessstress intensity test factor [MPa · m^(1/2)] Total work of 1283 13381198 fracture [J/m²] Molecular Mw 1,700,000 1,440,000 1,550,000 weightMn 390,000 340,000 410,000 Mw/Mn 4.4 4.3 3.7 Cutting workability A A ADenture Compression Manufacturing Cutting base test method of denturebase Yield point 2.3 2.7 2.5 strength [kN] Falling ball ManufacturingCutting test method of denture base Breaking ≥45.5 ≥45.5 45.5 weight [g]

—Description of Table 7—

“Angle” in the Charpy impact test indicates a swing angle (°) of apendulum after the pendulum hits a test piece

“Wt %” means % by mass with respect to total amount of a resin block(material for resin block).

As shown in Table 7, the materials for a denture base of Examples 1E to3E, which satisfy 110 MPa or more of flexural strength, 1.9 MPa·m^(1/2)or more of maximum stress intensity factor, and 900 J/m² or more oftotal work of fracture, were excellent in hardness (flexural modulus).Further, the denture bases, which were prepared using the materials ofExamples 1E to 3E, were excellent in the durability (yield pointstrength). Furthermore, the materials for a denture base of Examples 1Eto 3E were also excellent in the impact resistance, since the impactstrength is high. In addition, the materials for a denture baseexhibited excellent cutting workability.

In contrast, the materials for a denture base of Comparative Examples 1,3 and 6, which have a flexural strength less than 110 MPa, and have amaximum stress intensity factor less than 1.9 MPa·m^(1/2) or a totalwork of fracture less than 900 J/m², exhibited low hardness (flexuralmodulus) and impact resistance (impact strength). Further, the materialsfor a denture base of Comparative Examples 9 and 10, which have aflexural strength less than 110 MPa exhibited low hardness (flexuralmodulus). Furthermore, the denture bases, which were prepared using thematerials of Comparative Examples 1, 3, 6, 9, and 10 exhibited lowdurability (yield point strength).

Reference Example 3

As Reference Example 3, there is shown an example of a method ofestimating a flexural strength of a material for a denture base, whichwas used as a raw material of the denture base, using a denture base.

It is practically difficult to cut out a test piece having a length of39 mm, a height of 8 mm, and a width of 4 mm from the denture base.

However, when a minute fracture toughness test of a denture base isconducted as follows, a fracture toughness of the material for a denturebase used as a raw material of the denture base can be estimated.

—Minute Fracture Toughness Test—

A minute test piece having a length of 18.5 mm, a height of 4 mm, and awidth of 2 mm was cut out from a denture base, and then a slit of 1.5 mmdepth and a notch of from 50 to 200 μm were provided on the test piece.A minute fracture toughness test was carried out as described in thenormal fracture toughness test for a material for a denture base exceptthat the immersion into water was not carried out and the length of thesupport span was changed to 16 mm. The above fracture toughness test isreferred to as “minute fracture toughness test”, and the obtainedmaximum stress intensity factor and total work of fracture are referredto as “minute maximum stress intensity factor” and “minute total work offracture” respectively.

Regarding the denture bases of Examples 1E, 2E and 3E, the minutemaximum stress intensity factor and minute total work of fracture ofwere measured.

The obtained results are shown in the following Table 8.

TABLE 8 Minute maximum stress Maximum stress Minute total Total work ofintensity factor intensity factor work of fracture fracture of ofdenture base of denture base of denture base denture base [MPa ·m^(1/2)] [MPa · m^(1/2)] [J/m²] [J/m²] Example 1E 2.30 2.64 1045 1283Example 2E 2.36 2.67 1237 1338 Example 3E 2.18 2.49 993 1198

FIG. 4 is a graph showing an example of a relationship between a minutemaximum stress intensity factor of a denture base and a maximum stressintensity factor of a material for a denture base that was obtainedbased on the results shown in Table 8.

FIG. 5 is a graph showing an example of a relationship between a minutetotal work of fracture of a denture base and a total work of fracture ofa material for a denture base that was obtained based on the resultsshown in Table 8.

As shown in FIGS. 4 and 5, it was found that a maximum stress intensityfactor and a total work of fracture of a material for a denture base arein direct proportion to a minute maximum stress intensity factor and aminute total work of fracture of a material for a denture baserespectively. Therefore, it was found that the maximum stress intensityfactor and the total work of fracture of the material the denture basecan be estimated by measuring a minute maximum stress intensity factorand a minute total work of fracture of the denture base. In view ofenhancing the durability (yield point strength), for example, a minutemaximum stress intensity factor of a denture base is preferably 1.6MPa·m^(1/2) or more, and a minute total work of fracture of a denturebase is preferably 340 J/m² or more.

The entire disclosures of Japanese Patent Applications Nos. 2014-020634filed Feb. 5, 2014, 2014-265370 filed Dec. 26, 2014, 2016-255232 filedDec. 28, 2016, and 2017-250036 filed Dec. 26, 2017, are incorporated byreference in this specification.

All contents of the documents, patent applications, and technicalstandards described in this specification are incorporated herein byreference to the same extent as that when it is specifically andindividually described that the respective documents, patentapplications, and the technical standards are incorporated herein byreference.

The invention claimed is:
 1. A material for a denture base containing apolymer component containing an acrylic resin, wherein, when thematerial for a denture base is formed into a test piece having a lengthof 80 mm, a width of 10 mm, and a thickness of 4 mm, the test pieceexhibits 110 MPa or more of flexural strength measured by a three-pointflexural test in accordance with JIS K7171 (2008) under conditions of atesting speed of 2 mm/min and a length of a support span of 64 mm, andwherein, when the material for a denture base is formed into a notchedtest piece having a length of 39 mm, a height of 8 mm, and a width of 4mm, the test piece exhibits 1.9 MPa·m^(1/2) or more of maximum stressintensity factor measured by a fracture toughness test in accordancewith a flexural test in accordance with JIS T6501 (2012) under acondition of a testing speed of 1 mm/min, and exhibits 900 J/m² or moreof total work of fracture.
 2. The material for a denture base accordingto claim 1, wherein the flexural strength is 200 MPa or less.
 3. Thematerial for a denture base according to claim 1, wherein the maximumstress intensity factor is 3.5 MPa·m^(1/2) or less, and the total workof fracture is 2500 J/m² or less.
 4. The material for a denture baseaccording to claim 1, wherein, when the material for a denture base isformed into a single-notched test piece which is provided with a notchhaving a shape A prescribed by JIS K7111-1 (2012) and has a length of 80mm, a width of 10 mm, a remaining width of 8 mm, and a thickness of 4mm, the test piece exhibits 1.6 kJ/m² or more of impact strengthmeasured by a Charpy impact test under a condition of edgewise impact inaccordance with JIS K7111-1 (2012).
 5. The material for a denture baseaccording to claim 1, wherein a weight average molecular weight of thepolymer component is 1,200,000 or more.
 6. The material for a denturebase according to claim 1, wherein the polymer component furthercontains a rubber.
 7. The material for a denture base according to claim6, wherein the rubber contains a graft polymer obtained by graftpolymerization of a rubbery polymer having a cross-linked structure witha thermoplastic resin component.
 8. The material for a denture baseaccording to claim 6, wherein the rubber contains a graft polymerobtained by graft polymerization of a butadiene (co)polymer with athermoplastic resin component.
 9. The material for a denture baseaccording to claim 6, wherein a content of the rubber is from 1% by massto 10% by mass based on a total amount of the material for a denturebase.
 10. The material for a denture base according to claim 1, whereina content of the acrylic resin is 90% by mass or more based on a totalamount of the material for a denture base.
 11. The material for adenture base according to claim 1, wherein the acrylic resin is apolymer comprising a structural unit derived from a monofunctionalacrylic monomer in an amount of 95% by mass or more.
 12. The materialfor a denture base according to claim 11, wherein the monofunctionalacrylic monomer is at least one selected from the group consisting ofmethacrylic acid and methacrylic acid alkyl ester.
 13. The material fora denture base according to claim 11, wherein the monofunctional acrylicmonomer consists of methacrylic acid and methacrylic acid alkyl ester,and an amount of the methacrylic acid based on a total amount of themethacrylic acid and the methacrylic acid alkyl ester is from 0.1% bymass to 15% by mass.
 14. The material for a denture base according toclaim 1, wherein the acrylic resin is a co-polymer of methacrylic acidand methyl methacrylate.
 15. A denture base containing the material fora denture base according to claim
 1. 16. A plate denture comprising thedenture base according to claim 15 and an artificial tooth fixed to thedenture base.
 17. A method of manufacturing a denture base comprising astep of cutting the material for a denture base according to claim 1 toobtain a denture base.
 18. A method of manufacturing a plate denturecomprising: a step of cutting the material for a denture base accordingto claim 1 to obtain a denture base; and a step of fixing an artificialtooth to the denture base.